Update to tengo v2 (#976)

54 files changed, 17222 insertions, 0 deletions

diff --git a/vendor/github.com/d5/tengo/v2/.gitignore b/vendor/github.com/d5/tengo/v2/.gitignore
new file mode 100644
index 00000000..77738287
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/.gitignore
@@ -0,0 +1 @@
+dist/
\ No newline at end of file
diff --git a/vendor/github.com/d5/tengo/v2/.goreleaser.yml b/vendor/github.com/d5/tengo/v2/.goreleaser.yml
new file mode 100644
index 00000000..1bd14324
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/.goreleaser.yml
@@ -0,0 +1,20 @@
+env:
+  - GO111MODULE=on
+before:
+  hooks:
+    - go mod tidy
+builds:
+  - env:
+      - CGO_ENABLED=0
+    main: ./cmd/tengo/main.go
+    goos:
+      - darwin
+      - linux
+      - windows
+archive:
+  files:
+    - none*
+checksum:
+  name_template: 'checksums.txt'
+changelog:
+  sort: asc
diff --git a/vendor/github.com/d5/tengo/v2/LICENSE b/vendor/github.com/d5/tengo/v2/LICENSE
new file mode 100644
index 00000000..2516341a
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2019 Daniel Kang
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/vendor/github.com/d5/tengo/v2/Makefile b/vendor/github.com/d5/tengo/v2/Makefile
new file mode 100644
index 00000000..793bc129
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/Makefile
@@ -0,0 +1,11 @@
+generate:
+	go generate ./...
+
+lint:
+	golint -set_exit_status ./...
+
+test: generate lint
+	go test -race -cover ./...
+
+fmt:
+	go fmt ./...
diff --git a/vendor/github.com/d5/tengo/v2/README.md b/vendor/github.com/d5/tengo/v2/README.md
new file mode 100644
index 00000000..92277cfe
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/README.md
@@ -0,0 +1,135 @@
+<p align="center">
+  <img src="https://raw.githubusercontent.com/d5/tengolang-share/master/logo_400.png" width="200" height="200">
+</p>
+
+# The Tengo Language
+
+[![GoDoc](https://godoc.org/github.com/d5/tengo?status.svg)](https://godoc.org/github.com/d5/tengo)
+[![Go Report Card](https://goreportcard.com/badge/github.com/d5/tengo)](https://goreportcard.com/report/github.com/d5/tengo)
+[![CircleCI](https://circleci.com/gh/d5/tengo.svg?style=svg)](https://circleci.com/gh/d5/tengo)
+[![Sourcegraph](https://sourcegraph.com/github.com/d5/tengo/-/badge.svg)](https://sourcegraph.com/github.com/d5/tengo?badge)
+
+**Tengo is a small, dynamic, fast, secure script language for Go.** 
+
+Tengo is **[fast](#benchmark)** and secure because it's compiled/executed as
+bytecode on stack-based VM that's written in native Go.
+
+```golang
+/* The Tengo Language */
+fmt := import("fmt")
+
+each := func(seq, fn) {
+    for x in seq { fn(x) }
+}
+
+sum := func(init, seq) {
+    each(seq, func(x) { init += x })
+    return init
+}
+
+fmt.println(sum(0, [1, 2, 3]))   // "6"
+fmt.println(sum("", [1, 2, 3]))  // "123"
+```
+
+> Test this Tengo code in the
+> [Tengo Playground](https://tengolang.com/?s=0c8d5d0d88f2795a7093d7f35ae12c3afa17bea3)
+
+## Features
+
+- Simple and highly readable
+  [Syntax](https://github.com/d5/tengo/blob/master/docs/tutorial.md)
+  - Dynamic typing with type coercion
+  - Higher-order functions and closures
+  - Immutable values
+- [Securely Embeddable](https://github.com/d5/tengo/blob/master/docs/interoperability.md)
+  and [Extensible](https://github.com/d5/tengo/blob/master/docs/objects.md)
+- Compiler/runtime written in native Go _(no external deps or cgo)_
+- Executable as a
+  [standalone](https://github.com/d5/tengo/blob/master/docs/tengo-cli.md)
+  language / REPL
+- Use cases: rules engine, [state machine](https://github.com/d5/go-fsm),
+  data pipeline, [transpiler](https://github.com/d5/tengo2lua)
+
+## Benchmark
+
+| | fib(35) | fibt(35) |  Type  |
+| :--- |    ---: |     ---: |  :---: |
+| Go | `48ms` | `3ms` | Go (native) |
+| [**Tengo**](https://github.com/d5/tengo) | `2,349ms` | `5ms` | VM on Go |
+| Lua | `1,416ms` | `3ms` | Lua (native) |
+| [go-lua](https://github.com/Shopify/go-lua) | `4,402ms` | `5ms` | Lua VM on Go |
+| [GopherLua](https://github.com/yuin/gopher-lua) | `4,023ms` | `5ms` | Lua VM on Go |
+| Python | `2,588ms` | `26ms` | Python (native) |
+| [starlark-go](https://github.com/google/starlark-go) | `11,126ms` | `6ms` | Python-like Interpreter on Go |
+| [gpython](https://github.com/go-python/gpython) | `15,035ms` | `4ms` | Python Interpreter on Go |
+| [goja](https://github.com/dop251/goja) | `5,089ms` | `5ms` | JS VM on Go |
+| [otto](https://github.com/robertkrimen/otto) | `68,377ms` | `11ms` | JS Interpreter on Go |
+| [Anko](https://github.com/mattn/anko) | `92,579ms` | `18ms` | Interpreter on Go |
+
+_* [fib(35)](https://github.com/d5/tengobench/blob/master/code/fib.tengo):
+Fibonacci(35)_  
+_* [fibt(35)](https://github.com/d5/tengobench/blob/master/code/fibtc.tengo):
+[tail-call](https://en.wikipedia.org/wiki/Tail_call) version of Fibonacci(35)_  
+_* **Go** does not read the source code from file, while all other cases do_  
+_* See [here](https://github.com/d5/tengobench) for commands/codes used_
+
+## Quick Start
+
+A simple Go example code that compiles/runs Tengo script code with some input/output values:
+
+```golang
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/d5/tengo/v2"
+)
+
+func main() {
+	// Tengo script code
+	src := `
+each := func(seq, fn) {
+    for x in seq { fn(x) }
+}
+
+sum := 0
+mul := 1
+each([a, b, c, d], func(x) {
+	sum += x
+	mul *= x
+})`
+
+	// create a new Script instance
+	script := tengo.NewScript([]byte(src))
+
+	// set values
+	_ = script.Add("a", 1)
+	_ = script.Add("b", 9)
+	_ = script.Add("c", 8)
+	_ = script.Add("d", 4)
+
+	// run the script
+	compiled, err := script.RunContext(context.Background())
+	if err != nil {
+		panic(err)
+	}
+
+	// retrieve values
+	sum := compiled.Get("sum")
+	mul := compiled.Get("mul")
+	fmt.Println(sum, mul) // "22 288"
+}
+```
+
+## References
+
+- [Language Syntax](https://github.com/d5/tengo/blob/master/docs/tutorial.md)
+- [Object Types](https://github.com/d5/tengo/blob/master/docs/objects.md)
+- [Runtime Types](https://github.com/d5/tengo/blob/master/docs/runtime-types.md)
+  and [Operators](https://github.com/d5/tengo/blob/master/docs/operators.md)
+- [Builtin Functions](https://github.com/d5/tengo/blob/master/docs/builtins.md)
+- [Interoperability](https://github.com/d5/tengo/blob/master/docs/interoperability.md)
+- [Tengo CLI](https://github.com/d5/tengo/blob/master/docs/tengo-cli.md)
+- [Standard Library](https://github.com/d5/tengo/blob/master/docs/stdlib.md)
diff --git a/vendor/github.com/d5/tengo/v2/builtins.go b/vendor/github.com/d5/tengo/v2/builtins.go
new file mode 100644
index 00000000..87f7fc3d
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/builtins.go
@@ -0,0 +1,502 @@
+package tengo
+
+var builtinFuncs = []*BuiltinFunction{
+	{
+		Name:  "len",
+		Value: builtinLen,
+	},
+	{
+		Name:  "copy",
+		Value: builtinCopy,
+	},
+	{
+		Name:  "append",
+		Value: builtinAppend,
+	},
+	{
+		Name:  "string",
+		Value: builtinString,
+	},
+	{
+		Name:  "int",
+		Value: builtinInt,
+	},
+	{
+		Name:  "bool",
+		Value: builtinBool,
+	},
+	{
+		Name:  "float",
+		Value: builtinFloat,
+	},
+	{
+		Name:  "char",
+		Value: builtinChar,
+	},
+	{
+		Name:  "bytes",
+		Value: builtinBytes,
+	},
+	{
+		Name:  "time",
+		Value: builtinTime,
+	},
+	{
+		Name:  "is_int",
+		Value: builtinIsInt,
+	},
+	{
+		Name:  "is_float",
+		Value: builtinIsFloat,
+	},
+	{
+		Name:  "is_string",
+		Value: builtinIsString,
+	},
+	{
+		Name:  "is_bool",
+		Value: builtinIsBool,
+	},
+	{
+		Name:  "is_char",
+		Value: builtinIsChar,
+	},
+	{
+		Name:  "is_bytes",
+		Value: builtinIsBytes,
+	},
+	{
+		Name:  "is_array",
+		Value: builtinIsArray,
+	},
+	{
+		Name:  "is_immutable_array",
+		Value: builtinIsImmutableArray,
+	},
+	{
+		Name:  "is_map",
+		Value: builtinIsMap,
+	},
+	{
+		Name:  "is_immutable_map",
+		Value: builtinIsImmutableMap,
+	},
+	{
+		Name:  "is_iterable",
+		Value: builtinIsIterable,
+	},
+	{
+		Name:  "is_time",
+		Value: builtinIsTime,
+	},
+	{
+		Name:  "is_error",
+		Value: builtinIsError,
+	},
+	{
+		Name:  "is_undefined",
+		Value: builtinIsUndefined,
+	},
+	{
+		Name:  "is_function",
+		Value: builtinIsFunction,
+	},
+	{
+		Name:  "is_callable",
+		Value: builtinIsCallable,
+	},
+	{
+		Name:  "type_name",
+		Value: builtinTypeName,
+	},
+	{
+		Name:  "format",
+		Value: builtinFormat,
+	},
+}
+
+// GetAllBuiltinFunctions returns all builtin function objects.
+func GetAllBuiltinFunctions() []*BuiltinFunction {
+	return append([]*BuiltinFunction{}, builtinFuncs...)
+}
+
+func builtinTypeName(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	return &String{Value: args[0].TypeName()}, nil
+}
+
+func builtinIsString(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*String); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsInt(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Int); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsFloat(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Float); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsBool(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Bool); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsChar(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Char); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsBytes(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Bytes); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsArray(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Array); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsImmutableArray(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*ImmutableArray); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsMap(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Map); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsImmutableMap(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*ImmutableMap); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsTime(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Time); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsError(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Error); ok {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsUndefined(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if args[0] == UndefinedValue {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsFunction(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	switch args[0].(type) {
+	case *CompiledFunction:
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsCallable(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if args[0].CanCall() {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+func builtinIsIterable(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if args[0].CanIterate() {
+		return TrueValue, nil
+	}
+	return FalseValue, nil
+}
+
+// len(obj object) => int
+func builtinLen(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	switch arg := args[0].(type) {
+	case *Array:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *ImmutableArray:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *String:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *Bytes:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *Map:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	case *ImmutableMap:
+		return &Int{Value: int64(len(arg.Value))}, nil
+	default:
+		return nil, ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "array/string/bytes/map",
+			Found:    arg.TypeName(),
+		}
+	}
+}
+
+func builtinFormat(args ...Object) (Object, error) {
+	numArgs := len(args)
+	if numArgs == 0 {
+		return nil, ErrWrongNumArguments
+	}
+	format, ok := args[0].(*String)
+	if !ok {
+		return nil, ErrInvalidArgumentType{
+			Name:     "format",
+			Expected: "string",
+			Found:    args[0].TypeName(),
+		}
+	}
+	if numArgs == 1 {
+		// okay to return 'format' directly as String is immutable
+		return format, nil
+	}
+	s, err := Format(format.Value, args[1:]...)
+	if err != nil {
+		return nil, err
+	}
+	return &String{Value: s}, nil
+}
+
+func builtinCopy(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	return args[0].Copy(), nil
+}
+
+func builtinString(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*String); ok {
+		return args[0], nil
+	}
+	v, ok := ToString(args[0])
+	if ok {
+		if len(v) > MaxStringLen {
+			return nil, ErrStringLimit
+		}
+		return &String{Value: v}, nil
+	}
+	if argsLen == 2 {
+		return args[1], nil
+	}
+	return UndefinedValue, nil
+}
+
+func builtinInt(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Int); ok {
+		return args[0], nil
+	}
+	v, ok := ToInt64(args[0])
+	if ok {
+		return &Int{Value: v}, nil
+	}
+	if argsLen == 2 {
+		return args[1], nil
+	}
+	return UndefinedValue, nil
+}
+
+func builtinFloat(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Float); ok {
+		return args[0], nil
+	}
+	v, ok := ToFloat64(args[0])
+	if ok {
+		return &Float{Value: v}, nil
+	}
+	if argsLen == 2 {
+		return args[1], nil
+	}
+	return UndefinedValue, nil
+}
+
+func builtinBool(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Bool); ok {
+		return args[0], nil
+	}
+	v, ok := ToBool(args[0])
+	if ok {
+		if v {
+			return TrueValue, nil
+		}
+		return FalseValue, nil
+	}
+	return UndefinedValue, nil
+}
+
+func builtinChar(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Char); ok {
+		return args[0], nil
+	}
+	v, ok := ToRune(args[0])
+	if ok {
+		return &Char{Value: v}, nil
+	}
+	if argsLen == 2 {
+		return args[1], nil
+	}
+	return UndefinedValue, nil
+}
+
+func builtinBytes(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+
+	// bytes(N) => create a new bytes with given size N
+	if n, ok := args[0].(*Int); ok {
+		if n.Value > int64(MaxBytesLen) {
+			return nil, ErrBytesLimit
+		}
+		return &Bytes{Value: make([]byte, int(n.Value))}, nil
+	}
+	v, ok := ToByteSlice(args[0])
+	if ok {
+		if len(v) > MaxBytesLen {
+			return nil, ErrBytesLimit
+		}
+		return &Bytes{Value: v}, nil
+	}
+	if argsLen == 2 {
+		return args[1], nil
+	}
+	return UndefinedValue, nil
+}
+
+func builtinTime(args ...Object) (Object, error) {
+	argsLen := len(args)
+	if !(argsLen == 1 || argsLen == 2) {
+		return nil, ErrWrongNumArguments
+	}
+	if _, ok := args[0].(*Time); ok {
+		return args[0], nil
+	}
+	v, ok := ToTime(args[0])
+	if ok {
+		return &Time{Value: v}, nil
+	}
+	if argsLen == 2 {
+		return args[1], nil
+	}
+	return UndefinedValue, nil
+}
+
+// append(arr, items...)
+func builtinAppend(args ...Object) (Object, error) {
+	if len(args) < 2 {
+		return nil, ErrWrongNumArguments
+	}
+	switch arg := args[0].(type) {
+	case *Array:
+		return &Array{Value: append(arg.Value, args[1:]...)}, nil
+	case *ImmutableArray:
+		return &Array{Value: append(arg.Value, args[1:]...)}, nil
+	default:
+		return nil, ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "array",
+			Found:    arg.TypeName(),
+		}
+	}
+}
diff --git a/vendor/github.com/d5/tengo/v2/bytecode.go b/vendor/github.com/d5/tengo/v2/bytecode.go
new file mode 100644
index 00000000..cfd0d0b5
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/bytecode.go
@@ -0,0 +1,292 @@
+package tengo
+
+import (
+	"encoding/gob"
+	"fmt"
+	"io"
+	"reflect"
+
+	"github.com/d5/tengo/v2/parser"
+)
+
+// Bytecode is a compiled instructions and constants.
+type Bytecode struct {
+	FileSet      *parser.SourceFileSet
+	MainFunction *CompiledFunction
+	Constants    []Object
+}
+
+// Encode writes Bytecode data to the writer.
+func (b *Bytecode) Encode(w io.Writer) error {
+	enc := gob.NewEncoder(w)
+	if err := enc.Encode(b.FileSet); err != nil {
+		return err
+	}
+	if err := enc.Encode(b.MainFunction); err != nil {
+		return err
+	}
+	return enc.Encode(b.Constants)
+}
+
+// CountObjects returns the number of objects found in Constants.
+func (b *Bytecode) CountObjects() int {
+	n := 0
+	for _, c := range b.Constants {
+		n += CountObjects(c)
+	}
+	return n
+}
+
+// FormatInstructions returns human readable string representations of
+// compiled instructions.
+func (b *Bytecode) FormatInstructions() []string {
+	return FormatInstructions(b.MainFunction.Instructions, 0)
+}
+
+// FormatConstants returns human readable string representations of
+// compiled constants.
+func (b *Bytecode) FormatConstants() (output []string) {
+	for cidx, cn := range b.Constants {
+		switch cn := cn.(type) {
+		case *CompiledFunction:
+			output = append(output, fmt.Sprintf(
+				"[% 3d] (Compiled Function|%p)", cidx, &cn))
+			for _, l := range FormatInstructions(cn.Instructions, 0) {
+				output = append(output, fmt.Sprintf("     %s", l))
+			}
+		default:
+			output = append(output, fmt.Sprintf("[% 3d] %s (%s|%p)",
+				cidx, cn, reflect.TypeOf(cn).Elem().Name(), &cn))
+		}
+	}
+	return
+}
+
+// Decode reads Bytecode data from the reader.
+func (b *Bytecode) Decode(r io.Reader, modules *ModuleMap) error {
+	if modules == nil {
+		modules = NewModuleMap()
+	}
+
+	dec := gob.NewDecoder(r)
+	if err := dec.Decode(&b.FileSet); err != nil {
+		return err
+	}
+	// TODO: files in b.FileSet.File does not have their 'set' field properly
+	//  set to b.FileSet as it's private field and not serialized by gob
+	//  encoder/decoder.
+	if err := dec.Decode(&b.MainFunction); err != nil {
+		return err
+	}
+	if err := dec.Decode(&b.Constants); err != nil {
+		return err
+	}
+	for i, v := range b.Constants {
+		fv, err := fixDecodedObject(v, modules)
+		if err != nil {
+			return err
+		}
+		b.Constants[i] = fv
+	}
+	return nil
+}
+
+// RemoveDuplicates finds and remove the duplicate values in Constants.
+// Note this function mutates Bytecode.
+func (b *Bytecode) RemoveDuplicates() {
+	var deduped []Object
+
+	indexMap := make(map[int]int) // mapping from old constant index to new index
+	ints := make(map[int64]int)
+	strings := make(map[string]int)
+	floats := make(map[float64]int)
+	chars := make(map[rune]int)
+	immutableMaps := make(map[string]int) // for modules
+
+	for curIdx, c := range b.Constants {
+		switch c := c.(type) {
+		case *CompiledFunction:
+			// add to deduped list
+			indexMap[curIdx] = len(deduped)
+			deduped = append(deduped, c)
+		case *ImmutableMap:
+			modName := inferModuleName(c)
+			newIdx, ok := immutableMaps[modName]
+			if modName != "" && ok {
+				indexMap[curIdx] = newIdx
+			} else {
+				newIdx = len(deduped)
+				immutableMaps[modName] = newIdx
+				indexMap[curIdx] = newIdx
+				deduped = append(deduped, c)
+			}
+		case *Int:
+			if newIdx, ok := ints[c.Value]; ok {
+				indexMap[curIdx] = newIdx
+			} else {
+				newIdx = len(deduped)
+				ints[c.Value] = newIdx
+				indexMap[curIdx] = newIdx
+				deduped = append(deduped, c)
+			}
+		case *String:
+			if newIdx, ok := strings[c.Value]; ok {
+				indexMap[curIdx] = newIdx
+			} else {
+				newIdx = len(deduped)
+				strings[c.Value] = newIdx
+				indexMap[curIdx] = newIdx
+				deduped = append(deduped, c)
+			}
+		case *Float:
+			if newIdx, ok := floats[c.Value]; ok {
+				indexMap[curIdx] = newIdx
+			} else {
+				newIdx = len(deduped)
+				floats[c.Value] = newIdx
+				indexMap[curIdx] = newIdx
+				deduped = append(deduped, c)
+			}
+		case *Char:
+			if newIdx, ok := chars[c.Value]; ok {
+				indexMap[curIdx] = newIdx
+			} else {
+				newIdx = len(deduped)
+				chars[c.Value] = newIdx
+				indexMap[curIdx] = newIdx
+				deduped = append(deduped, c)
+			}
+		default:
+			panic(fmt.Errorf("unsupported top-level constant type: %s",
+				c.TypeName()))
+		}
+	}
+
+	// replace with de-duplicated constants
+	b.Constants = deduped
+
+	// update CONST instructions with new indexes
+	// main function
+	updateConstIndexes(b.MainFunction.Instructions, indexMap)
+	// other compiled functions in constants
+	for _, c := range b.Constants {
+		switch c := c.(type) {
+		case *CompiledFunction:
+			updateConstIndexes(c.Instructions, indexMap)
+		}
+	}
+}
+
+func fixDecodedObject(
+	o Object,
+	modules *ModuleMap,
+) (Object, error) {
+	switch o := o.(type) {
+	case *Bool:
+		if o.IsFalsy() {
+			return FalseValue, nil
+		}
+		return TrueValue, nil
+	case *Undefined:
+		return UndefinedValue, nil
+	case *Array:
+		for i, v := range o.Value {
+			fv, err := fixDecodedObject(v, modules)
+			if err != nil {
+				return nil, err
+			}
+			o.Value[i] = fv
+		}
+	case *ImmutableArray:
+		for i, v := range o.Value {
+			fv, err := fixDecodedObject(v, modules)
+			if err != nil {
+				return nil, err
+			}
+			o.Value[i] = fv
+		}
+	case *Map:
+		for k, v := range o.Value {
+			fv, err := fixDecodedObject(v, modules)
+			if err != nil {
+				return nil, err
+			}
+			o.Value[k] = fv
+		}
+	case *ImmutableMap:
+		modName := inferModuleName(o)
+		if mod := modules.GetBuiltinModule(modName); mod != nil {
+			return mod.AsImmutableMap(modName), nil
+		}
+
+		for k, v := range o.Value {
+			// encoding of user function not supported
+			if _, isUserFunction := v.(*UserFunction); isUserFunction {
+				return nil, fmt.Errorf("user function not decodable")
+			}
+
+			fv, err := fixDecodedObject(v, modules)
+			if err != nil {
+				return nil, err
+			}
+			o.Value[k] = fv
+		}
+	}
+	return o, nil
+}
+
+func updateConstIndexes(insts []byte, indexMap map[int]int) {
+	i := 0
+	for i < len(insts) {
+		op := insts[i]
+		numOperands := parser.OpcodeOperands[op]
+		_, read := parser.ReadOperands(numOperands, insts[i+1:])
+
+		switch op {
+		case parser.OpConstant:
+			curIdx := int(insts[i+2]) | int(insts[i+1])<<8
+			newIdx, ok := indexMap[curIdx]
+			if !ok {
+				panic(fmt.Errorf("constant index not found: %d", curIdx))
+			}
+			copy(insts[i:], MakeInstruction(op, newIdx))
+		case parser.OpClosure:
+			curIdx := int(insts[i+2]) | int(insts[i+1])<<8
+			numFree := int(insts[i+3])
+			newIdx, ok := indexMap[curIdx]
+			if !ok {
+				panic(fmt.Errorf("constant index not found: %d", curIdx))
+			}
+			copy(insts[i:], MakeInstruction(op, newIdx, numFree))
+		}
+
+		i += 1 + read
+	}
+}
+
+func inferModuleName(mod *ImmutableMap) string {
+	if modName, ok := mod.Value["__module_name__"].(*String); ok {
+		return modName.Value
+	}
+	return ""
+}
+
+func init() {
+	gob.Register(&parser.SourceFileSet{})
+	gob.Register(&parser.SourceFile{})
+	gob.Register(&Array{})
+	gob.Register(&Bool{})
+	gob.Register(&Bytes{})
+	gob.Register(&Char{})
+	gob.Register(&CompiledFunction{})
+	gob.Register(&Error{})
+	gob.Register(&Float{})
+	gob.Register(&ImmutableArray{})
+	gob.Register(&ImmutableMap{})
+	gob.Register(&Int{})
+	gob.Register(&Map{})
+	gob.Register(&String{})
+	gob.Register(&Time{})
+	gob.Register(&Undefined{})
+	gob.Register(&UserFunction{})
+}
diff --git a/vendor/github.com/d5/tengo/v2/compiler.go b/vendor/github.com/d5/tengo/v2/compiler.go
new file mode 100644
index 00000000..eb686ed6
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/compiler.go
@@ -0,0 +1,1312 @@
+package tengo
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"path/filepath"
+	"reflect"
+	"strings"
+
+	"github.com/d5/tengo/v2/parser"
+	"github.com/d5/tengo/v2/token"
+)
+
+// compilationScope represents a compiled instructions and the last two
+// instructions that were emitted.
+type compilationScope struct {
+	Instructions []byte
+	SymbolInit   map[string]bool
+	SourceMap    map[int]parser.Pos
+}
+
+// loop represents a loop construct that the compiler uses to track the current
+// loop.
+type loop struct {
+	Continues []int
+	Breaks    []int
+}
+
+// CompilerError represents a compiler error.
+type CompilerError struct {
+	FileSet *parser.SourceFileSet
+	Node    parser.Node
+	Err     error
+}
+
+func (e *CompilerError) Error() string {
+	filePos := e.FileSet.Position(e.Node.Pos())
+	return fmt.Sprintf("Compile Error: %s\n\tat %s", e.Err.Error(), filePos)
+}
+
+// Compiler compiles the AST into a bytecode.
+type Compiler struct {
+	file            *parser.SourceFile
+	parent          *Compiler
+	modulePath      string
+	constants       []Object
+	symbolTable     *SymbolTable
+	scopes          []compilationScope
+	scopeIndex      int
+	modules         *ModuleMap
+	compiledModules map[string]*CompiledFunction
+	allowFileImport bool
+	loops           []*loop
+	loopIndex       int
+	trace           io.Writer
+	indent          int
+}
+
+// NewCompiler creates a Compiler.
+func NewCompiler(
+	file *parser.SourceFile,
+	symbolTable *SymbolTable,
+	constants []Object,
+	modules *ModuleMap,
+	trace io.Writer,
+) *Compiler {
+	mainScope := compilationScope{
+		SymbolInit: make(map[string]bool),
+		SourceMap:  make(map[int]parser.Pos),
+	}
+
+	// symbol table
+	if symbolTable == nil {
+		symbolTable = NewSymbolTable()
+	}
+
+	// add builtin functions to the symbol table
+	for idx, fn := range builtinFuncs {
+		symbolTable.DefineBuiltin(idx, fn.Name)
+	}
+
+	// builtin modules
+	if modules == nil {
+		modules = NewModuleMap()
+	}
+
+	return &Compiler{
+		file:            file,
+		symbolTable:     symbolTable,
+		constants:       constants,
+		scopes:          []compilationScope{mainScope},
+		scopeIndex:      0,
+		loopIndex:       -1,
+		trace:           trace,
+		modules:         modules,
+		compiledModules: make(map[string]*CompiledFunction),
+	}
+}
+
+// Compile compiles the AST node.
+func (c *Compiler) Compile(node parser.Node) error {
+	if c.trace != nil {
+		if node != nil {
+			defer untracec(tracec(c, fmt.Sprintf("%s (%s)",
+				node.String(), reflect.TypeOf(node).Elem().Name())))
+		} else {
+			defer untracec(tracec(c, "<nil>"))
+		}
+	}
+
+	switch node := node.(type) {
+	case *parser.File:
+		for _, stmt := range node.Stmts {
+			if err := c.Compile(stmt); err != nil {
+				return err
+			}
+		}
+	case *parser.ExprStmt:
+		if err := c.Compile(node.Expr); err != nil {
+			return err
+		}
+		c.emit(node, parser.OpPop)
+	case *parser.IncDecStmt:
+		op := token.AddAssign
+		if node.Token == token.Dec {
+			op = token.SubAssign
+		}
+		return c.compileAssign(node, []parser.Expr{node.Expr},
+			[]parser.Expr{&parser.IntLit{Value: 1}}, op)
+	case *parser.ParenExpr:
+		if err := c.Compile(node.Expr); err != nil {
+			return err
+		}
+	case *parser.BinaryExpr:
+		if node.Token == token.LAnd || node.Token == token.LOr {
+			return c.compileLogical(node)
+		}
+		if node.Token == token.Less {
+			if err := c.Compile(node.RHS); err != nil {
+				return err
+			}
+			if err := c.Compile(node.LHS); err != nil {
+				return err
+			}
+			c.emit(node, parser.OpBinaryOp, int(token.Greater))
+			return nil
+		} else if node.Token == token.LessEq {
+			if err := c.Compile(node.RHS); err != nil {
+				return err
+			}
+			if err := c.Compile(node.LHS); err != nil {
+				return err
+			}
+			c.emit(node, parser.OpBinaryOp, int(token.GreaterEq))
+			return nil
+		}
+		if err := c.Compile(node.LHS); err != nil {
+			return err
+		}
+		if err := c.Compile(node.RHS); err != nil {
+			return err
+		}
+
+		switch node.Token {
+		case token.Add:
+			c.emit(node, parser.OpBinaryOp, int(token.Add))
+		case token.Sub:
+			c.emit(node, parser.OpBinaryOp, int(token.Sub))
+		case token.Mul:
+			c.emit(node, parser.OpBinaryOp, int(token.Mul))
+		case token.Quo:
+			c.emit(node, parser.OpBinaryOp, int(token.Quo))
+		case token.Rem:
+			c.emit(node, parser.OpBinaryOp, int(token.Rem))
+		case token.Greater:
+			c.emit(node, parser.OpBinaryOp, int(token.Greater))
+		case token.GreaterEq:
+			c.emit(node, parser.OpBinaryOp, int(token.GreaterEq))
+		case token.Equal:
+			c.emit(node, parser.OpEqual)
+		case token.NotEqual:
+			c.emit(node, parser.OpNotEqual)
+		case token.And:
+			c.emit(node, parser.OpBinaryOp, int(token.And))
+		case token.Or:
+			c.emit(node, parser.OpBinaryOp, int(token.Or))
+		case token.Xor:
+			c.emit(node, parser.OpBinaryOp, int(token.Xor))
+		case token.AndNot:
+			c.emit(node, parser.OpBinaryOp, int(token.AndNot))
+		case token.Shl:
+			c.emit(node, parser.OpBinaryOp, int(token.Shl))
+		case token.Shr:
+			c.emit(node, parser.OpBinaryOp, int(token.Shr))
+		default:
+			return c.errorf(node, "invalid binary operator: %s",
+				node.Token.String())
+		}
+	case *parser.IntLit:
+		c.emit(node, parser.OpConstant,
+			c.addConstant(&Int{Value: node.Value}))
+	case *parser.FloatLit:
+		c.emit(node, parser.OpConstant,
+			c.addConstant(&Float{Value: node.Value}))
+	case *parser.BoolLit:
+		if node.Value {
+			c.emit(node, parser.OpTrue)
+		} else {
+			c.emit(node, parser.OpFalse)
+		}
+	case *parser.StringLit:
+		if len(node.Value) > MaxStringLen {
+			return c.error(node, ErrStringLimit)
+		}
+		c.emit(node, parser.OpConstant,
+			c.addConstant(&String{Value: node.Value}))
+	case *parser.CharLit:
+		c.emit(node, parser.OpConstant,
+			c.addConstant(&Char{Value: node.Value}))
+	case *parser.UndefinedLit:
+		c.emit(node, parser.OpNull)
+	case *parser.UnaryExpr:
+		if err := c.Compile(node.Expr); err != nil {
+			return err
+		}
+
+		switch node.Token {
+		case token.Not:
+			c.emit(node, parser.OpLNot)
+		case token.Sub:
+			c.emit(node, parser.OpMinus)
+		case token.Xor:
+			c.emit(node, parser.OpBComplement)
+		case token.Add:
+			// do nothing?
+		default:
+			return c.errorf(node,
+				"invalid unary operator: %s", node.Token.String())
+		}
+	case *parser.IfStmt:
+		// open new symbol table for the statement
+		c.symbolTable = c.symbolTable.Fork(true)
+		defer func() {
+			c.symbolTable = c.symbolTable.Parent(false)
+		}()
+
+		if node.Init != nil {
+			if err := c.Compile(node.Init); err != nil {
+				return err
+			}
+		}
+		if err := c.Compile(node.Cond); err != nil {
+			return err
+		}
+
+		// first jump placeholder
+		jumpPos1 := c.emit(node, parser.OpJumpFalsy, 0)
+		if err := c.Compile(node.Body); err != nil {
+			return err
+		}
+		if node.Else != nil {
+			// second jump placeholder
+			jumpPos2 := c.emit(node, parser.OpJump, 0)
+
+			// update first jump offset
+			curPos := len(c.currentInstructions())
+			c.changeOperand(jumpPos1, curPos)
+			if err := c.Compile(node.Else); err != nil {
+				return err
+			}
+
+			// update second jump offset
+			curPos = len(c.currentInstructions())
+			c.changeOperand(jumpPos2, curPos)
+		} else {
+			// update first jump offset
+			curPos := len(c.currentInstructions())
+			c.changeOperand(jumpPos1, curPos)
+		}
+	case *parser.ForStmt:
+		return c.compileForStmt(node)
+	case *parser.ForInStmt:
+		return c.compileForInStmt(node)
+	case *parser.BranchStmt:
+		if node.Token == token.Break {
+			curLoop := c.currentLoop()
+			if curLoop == nil {
+				return c.errorf(node, "break not allowed outside loop")
+			}
+			pos := c.emit(node, parser.OpJump, 0)
+			curLoop.Breaks = append(curLoop.Breaks, pos)
+		} else if node.Token == token.Continue {
+			curLoop := c.currentLoop()
+			if curLoop == nil {
+				return c.errorf(node, "continue not allowed outside loop")
+			}
+			pos := c.emit(node, parser.OpJump, 0)
+			curLoop.Continues = append(curLoop.Continues, pos)
+		} else {
+			panic(fmt.Errorf("invalid branch statement: %s",
+				node.Token.String()))
+		}
+	case *parser.BlockStmt:
+		if len(node.Stmts) == 0 {
+			return nil
+		}
+
+		c.symbolTable = c.symbolTable.Fork(true)
+		defer func() {
+			c.symbolTable = c.symbolTable.Parent(false)
+		}()
+
+		for _, stmt := range node.Stmts {
+			if err := c.Compile(stmt); err != nil {
+				return err
+			}
+		}
+	case *parser.AssignStmt:
+		err := c.compileAssign(node, node.LHS, node.RHS, node.Token)
+		if err != nil {
+			return err
+		}
+	case *parser.Ident:
+		symbol, _, ok := c.symbolTable.Resolve(node.Name)
+		if !ok {
+			return c.errorf(node, "unresolved reference '%s'", node.Name)
+		}
+
+		switch symbol.Scope {
+		case ScopeGlobal:
+			c.emit(node, parser.OpGetGlobal, symbol.Index)
+		case ScopeLocal:
+			c.emit(node, parser.OpGetLocal, symbol.Index)
+		case ScopeBuiltin:
+			c.emit(node, parser.OpGetBuiltin, symbol.Index)
+		case ScopeFree:
+			c.emit(node, parser.OpGetFree, symbol.Index)
+		}
+	case *parser.ArrayLit:
+		for _, elem := range node.Elements {
+			if err := c.Compile(elem); err != nil {
+				return err
+			}
+		}
+		c.emit(node, parser.OpArray, len(node.Elements))
+	case *parser.MapLit:
+		for _, elt := range node.Elements {
+			// key
+			if len(elt.Key) > MaxStringLen {
+				return c.error(node, ErrStringLimit)
+			}
+			c.emit(node, parser.OpConstant,
+				c.addConstant(&String{Value: elt.Key}))
+
+			// value
+			if err := c.Compile(elt.Value); err != nil {
+				return err
+			}
+		}
+		c.emit(node, parser.OpMap, len(node.Elements)*2)
+
+	case *parser.SelectorExpr: // selector on RHS side
+		if err := c.Compile(node.Expr); err != nil {
+			return err
+		}
+		if err := c.Compile(node.Sel); err != nil {
+			return err
+		}
+		c.emit(node, parser.OpIndex)
+	case *parser.IndexExpr:
+		if err := c.Compile(node.Expr); err != nil {
+			return err
+		}
+		if err := c.Compile(node.Index); err != nil {
+			return err
+		}
+		c.emit(node, parser.OpIndex)
+	case *parser.SliceExpr:
+		if err := c.Compile(node.Expr); err != nil {
+			return err
+		}
+		if node.Low != nil {
+			if err := c.Compile(node.Low); err != nil {
+				return err
+			}
+		} else {
+			c.emit(node, parser.OpNull)
+		}
+		if node.High != nil {
+			if err := c.Compile(node.High); err != nil {
+				return err
+			}
+		} else {
+			c.emit(node, parser.OpNull)
+		}
+		c.emit(node, parser.OpSliceIndex)
+	case *parser.FuncLit:
+		c.enterScope()
+
+		for _, p := range node.Type.Params.List {
+			s := c.symbolTable.Define(p.Name)
+
+			// function arguments is not assigned directly.
+			s.LocalAssigned = true
+		}
+
+		if err := c.Compile(node.Body); err != nil {
+			return err
+		}
+
+		// code optimization
+		c.optimizeFunc(node)
+
+		freeSymbols := c.symbolTable.FreeSymbols()
+		numLocals := c.symbolTable.MaxSymbols()
+		instructions, sourceMap := c.leaveScope()
+
+		for _, s := range freeSymbols {
+			switch s.Scope {
+			case ScopeLocal:
+				if !s.LocalAssigned {
+					// Here, the closure is capturing a local variable that's
+					// not yet assigned its value. One example is a local
+					// recursive function:
+					//
+					//   func() {
+					//     foo := func(x) {
+					//       // ..
+					//       return foo(x-1)
+					//     }
+					//   }
+					//
+					// which translate into
+					//
+					//   0000 GETL    0
+					//   0002 CLOSURE ?     1
+					//   0006 DEFL    0
+					//
+					// . So the local variable (0) is being captured before
+					// it's assigned the value.
+					//
+					// Solution is to transform the code into something like
+					// this:
+					//
+					//   func() {
+					//     foo := undefined
+					//     foo = func(x) {
+					//       // ..
+					//       return foo(x-1)
+					//     }
+					//   }
+					//
+					// that is equivalent to
+					//
+					//   0000 NULL
+					//   0001 DEFL    0
+					//   0003 GETL    0
+					//   0005 CLOSURE ?     1
+					//   0009 SETL    0
+					//
+					c.emit(node, parser.OpNull)
+					c.emit(node, parser.OpDefineLocal, s.Index)
+					s.LocalAssigned = true
+				}
+				c.emit(node, parser.OpGetLocalPtr, s.Index)
+			case ScopeFree:
+				c.emit(node, parser.OpGetFreePtr, s.Index)
+			}
+		}
+
+		compiledFunction := &CompiledFunction{
+			Instructions:  instructions,
+			NumLocals:     numLocals,
+			NumParameters: len(node.Type.Params.List),
+			VarArgs:       node.Type.Params.VarArgs,
+			SourceMap:     sourceMap,
+		}
+		if len(freeSymbols) > 0 {
+			c.emit(node, parser.OpClosure,
+				c.addConstant(compiledFunction), len(freeSymbols))
+		} else {
+			c.emit(node, parser.OpConstant, c.addConstant(compiledFunction))
+		}
+	case *parser.ReturnStmt:
+		if c.symbolTable.Parent(true) == nil {
+			// outside the function
+			return c.errorf(node, "return not allowed outside function")
+		}
+
+		if node.Result == nil {
+			c.emit(node, parser.OpReturn, 0)
+		} else {
+			if err := c.Compile(node.Result); err != nil {
+				return err
+			}
+			c.emit(node, parser.OpReturn, 1)
+		}
+	case *parser.CallExpr:
+		if err := c.Compile(node.Func); err != nil {
+			return err
+		}
+		for _, arg := range node.Args {
+			if err := c.Compile(arg); err != nil {
+				return err
+			}
+		}
+		c.emit(node, parser.OpCall, len(node.Args))
+	case *parser.ImportExpr:
+		if node.ModuleName == "" {
+			return c.errorf(node, "empty module name")
+		}
+
+		if mod := c.modules.Get(node.ModuleName); mod != nil {
+			v, err := mod.Import(node.ModuleName)
+			if err != nil {
+				return err
+			}
+
+			switch v := v.(type) {
+			case []byte: // module written in Tengo
+				compiled, err := c.compileModule(node,
+					node.ModuleName, node.ModuleName, v)
+				if err != nil {
+					return err
+				}
+				c.emit(node, parser.OpConstant, c.addConstant(compiled))
+				c.emit(node, parser.OpCall, 0)
+			case Object: // builtin module
+				c.emit(node, parser.OpConstant, c.addConstant(v))
+			default:
+				panic(fmt.Errorf("invalid import value type: %T", v))
+			}
+		} else if c.allowFileImport {
+			moduleName := node.ModuleName
+			if !strings.HasSuffix(moduleName, ".tengo") {
+				moduleName += ".tengo"
+			}
+
+			modulePath, err := filepath.Abs(moduleName)
+			if err != nil {
+				return c.errorf(node, "module file path error: %s",
+					err.Error())
+			}
+
+			if err := c.checkCyclicImports(node, modulePath); err != nil {
+				return err
+			}
+
+			moduleSrc, err := ioutil.ReadFile(moduleName)
+			if err != nil {
+				return c.errorf(node, "module file read error: %s",
+					err.Error())
+			}
+
+			compiled, err := c.compileModule(node,
+				moduleName, modulePath, moduleSrc)
+			if err != nil {
+				return err
+			}
+			c.emit(node, parser.OpConstant, c.addConstant(compiled))
+			c.emit(node, parser.OpCall, 0)
+		} else {
+			return c.errorf(node, "module '%s' not found", node.ModuleName)
+		}
+	case *parser.ExportStmt:
+		// export statement must be in top-level scope
+		if c.scopeIndex != 0 {
+			return c.errorf(node, "export not allowed inside function")
+		}
+
+		// export statement is simply ignore when compiling non-module code
+		if c.parent == nil {
+			break
+		}
+		if err := c.Compile(node.Result); err != nil {
+			return err
+		}
+		c.emit(node, parser.OpImmutable)
+		c.emit(node, parser.OpReturn, 1)
+	case *parser.ErrorExpr:
+		if err := c.Compile(node.Expr); err != nil {
+			return err
+		}
+		c.emit(node, parser.OpError)
+	case *parser.ImmutableExpr:
+		if err := c.Compile(node.Expr); err != nil {
+			return err
+		}
+		c.emit(node, parser.OpImmutable)
+	case *parser.CondExpr:
+		if err := c.Compile(node.Cond); err != nil {
+			return err
+		}
+
+		// first jump placeholder
+		jumpPos1 := c.emit(node, parser.OpJumpFalsy, 0)
+		if err := c.Compile(node.True); err != nil {
+			return err
+		}
+
+		// second jump placeholder
+		jumpPos2 := c.emit(node, parser.OpJump, 0)
+
+		// update first jump offset
+		curPos := len(c.currentInstructions())
+		c.changeOperand(jumpPos1, curPos)
+		if err := c.Compile(node.False); err != nil {
+			return err
+		}
+
+		// update second jump offset
+		curPos = len(c.currentInstructions())
+		c.changeOperand(jumpPos2, curPos)
+	}
+	return nil
+}
+
+// Bytecode returns a compiled bytecode.
+func (c *Compiler) Bytecode() *Bytecode {
+	return &Bytecode{
+		FileSet: c.file.Set(),
+		MainFunction: &CompiledFunction{
+			Instructions: append(c.currentInstructions(), parser.OpSuspend),
+			SourceMap:    c.currentSourceMap(),
+		},
+		Constants: c.constants,
+	}
+}
+
+// EnableFileImport enables or disables module loading from local files.
+// Local file modules are disabled by default.
+func (c *Compiler) EnableFileImport(enable bool) {
+	c.allowFileImport = enable
+}
+
+func (c *Compiler) compileAssign(
+	node parser.Node,
+	lhs, rhs []parser.Expr,
+	op token.Token,
+) error {
+	numLHS, numRHS := len(lhs), len(rhs)
+	if numLHS > 1 || numRHS > 1 {
+		return c.errorf(node, "tuple assignment not allowed")
+	}
+
+	// resolve and compile left-hand side
+	ident, selectors := resolveAssignLHS(lhs[0])
+	numSel := len(selectors)
+
+	if op == token.Define && numSel > 0 {
+		// using selector on new variable does not make sense
+		return c.errorf(node, "operator ':=' not allowed with selector")
+	}
+
+	symbol, depth, exists := c.symbolTable.Resolve(ident)
+	if op == token.Define {
+		if depth == 0 && exists {
+			return c.errorf(node, "'%s' redeclared in this block", ident)
+		}
+		symbol = c.symbolTable.Define(ident)
+	} else {
+		if !exists {
+			return c.errorf(node, "unresolved reference '%s'", ident)
+		}
+	}
+
+	// +=, -=, *=, /=
+	if op != token.Assign && op != token.Define {
+		if err := c.Compile(lhs[0]); err != nil {
+			return err
+		}
+	}
+
+	// compile RHSs
+	for _, expr := range rhs {
+		if err := c.Compile(expr); err != nil {
+			return err
+		}
+	}
+
+	switch op {
+	case token.AddAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.Add))
+	case token.SubAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.Sub))
+	case token.MulAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.Mul))
+	case token.QuoAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.Quo))
+	case token.RemAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.Rem))
+	case token.AndAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.And))
+	case token.OrAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.Or))
+	case token.AndNotAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.AndNot))
+	case token.XorAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.Xor))
+	case token.ShlAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.Shl))
+	case token.ShrAssign:
+		c.emit(node, parser.OpBinaryOp, int(token.Shr))
+	}
+
+	// compile selector expressions (right to left)
+	for i := numSel - 1; i >= 0; i-- {
+		if err := c.Compile(selectors[i]); err != nil {
+			return err
+		}
+	}
+
+	switch symbol.Scope {
+	case ScopeGlobal:
+		if numSel > 0 {
+			c.emit(node, parser.OpSetSelGlobal, symbol.Index, numSel)
+		} else {
+			c.emit(node, parser.OpSetGlobal, symbol.Index)
+		}
+	case ScopeLocal:
+		if numSel > 0 {
+			c.emit(node, parser.OpSetSelLocal, symbol.Index, numSel)
+		} else {
+			if op == token.Define && !symbol.LocalAssigned {
+				c.emit(node, parser.OpDefineLocal, symbol.Index)
+			} else {
+				c.emit(node, parser.OpSetLocal, symbol.Index)
+			}
+		}
+
+		// mark the symbol as local-assigned
+		symbol.LocalAssigned = true
+	case ScopeFree:
+		if numSel > 0 {
+			c.emit(node, parser.OpSetSelFree, symbol.Index, numSel)
+		} else {
+			c.emit(node, parser.OpSetFree, symbol.Index)
+		}
+	default:
+		panic(fmt.Errorf("invalid assignment variable scope: %s",
+			symbol.Scope))
+	}
+	return nil
+}
+
+func (c *Compiler) compileLogical(node *parser.BinaryExpr) error {
+	// left side term
+	if err := c.Compile(node.LHS); err != nil {
+		return err
+	}
+
+	// jump position
+	var jumpPos int
+	if node.Token == token.LAnd {
+		jumpPos = c.emit(node, parser.OpAndJump, 0)
+	} else {
+		jumpPos = c.emit(node, parser.OpOrJump, 0)
+	}
+
+	// right side term
+	if err := c.Compile(node.RHS); err != nil {
+		return err
+	}
+
+	c.changeOperand(jumpPos, len(c.currentInstructions()))
+	return nil
+}
+
+func (c *Compiler) compileForStmt(stmt *parser.ForStmt) error {
+	c.symbolTable = c.symbolTable.Fork(true)
+	defer func() {
+		c.symbolTable = c.symbolTable.Parent(false)
+	}()
+
+	// init statement
+	if stmt.Init != nil {
+		if err := c.Compile(stmt.Init); err != nil {
+			return err
+		}
+	}
+
+	// pre-condition position
+	preCondPos := len(c.currentInstructions())
+
+	// condition expression
+	postCondPos := -1
+	if stmt.Cond != nil {
+		if err := c.Compile(stmt.Cond); err != nil {
+			return err
+		}
+		// condition jump position
+		postCondPos = c.emit(stmt, parser.OpJumpFalsy, 0)
+	}
+
+	// enter loop
+	loop := c.enterLoop()
+
+	// body statement
+	if err := c.Compile(stmt.Body); err != nil {
+		c.leaveLoop()
+		return err
+	}
+
+	c.leaveLoop()
+
+	// post-body position
+	postBodyPos := len(c.currentInstructions())
+
+	// post statement
+	if stmt.Post != nil {
+		if err := c.Compile(stmt.Post); err != nil {
+			return err
+		}
+	}
+
+	// back to condition
+	c.emit(stmt, parser.OpJump, preCondPos)
+
+	// post-statement position
+	postStmtPos := len(c.currentInstructions())
+	if postCondPos >= 0 {
+		c.changeOperand(postCondPos, postStmtPos)
+	}
+
+	// update all break/continue jump positions
+	for _, pos := range loop.Breaks {
+		c.changeOperand(pos, postStmtPos)
+	}
+	for _, pos := range loop.Continues {
+		c.changeOperand(pos, postBodyPos)
+	}
+	return nil
+}
+
+func (c *Compiler) compileForInStmt(stmt *parser.ForInStmt) error {
+	c.symbolTable = c.symbolTable.Fork(true)
+	defer func() {
+		c.symbolTable = c.symbolTable.Parent(false)
+	}()
+
+	// for-in statement is compiled like following:
+	//
+	//   for :it := iterator(iterable); :it.next();  {
+	//     k, v := :it.get()  // DEFINE operator
+	//
+	//     ... body ...
+	//   }
+	//
+	// ":it" is a local variable but will be conflict with other user variables
+	// because character ":" is not allowed.
+
+	// init
+	//   :it = iterator(iterable)
+	itSymbol := c.symbolTable.Define(":it")
+	if err := c.Compile(stmt.Iterable); err != nil {
+		return err
+	}
+	c.emit(stmt, parser.OpIteratorInit)
+	if itSymbol.Scope == ScopeGlobal {
+		c.emit(stmt, parser.OpSetGlobal, itSymbol.Index)
+	} else {
+		c.emit(stmt, parser.OpDefineLocal, itSymbol.Index)
+	}
+
+	// pre-condition position
+	preCondPos := len(c.currentInstructions())
+
+	// condition
+	//  :it.HasMore()
+	if itSymbol.Scope == ScopeGlobal {
+		c.emit(stmt, parser.OpGetGlobal, itSymbol.Index)
+	} else {
+		c.emit(stmt, parser.OpGetLocal, itSymbol.Index)
+	}
+	c.emit(stmt, parser.OpIteratorNext)
+
+	// condition jump position
+	postCondPos := c.emit(stmt, parser.OpJumpFalsy, 0)
+
+	// enter loop
+	loop := c.enterLoop()
+
+	// assign key variable
+	if stmt.Key.Name != "_" {
+		keySymbol := c.symbolTable.Define(stmt.Key.Name)
+		if itSymbol.Scope == ScopeGlobal {
+			c.emit(stmt, parser.OpGetGlobal, itSymbol.Index)
+		} else {
+			c.emit(stmt, parser.OpGetLocal, itSymbol.Index)
+		}
+		c.emit(stmt, parser.OpIteratorKey)
+		if keySymbol.Scope == ScopeGlobal {
+			c.emit(stmt, parser.OpSetGlobal, keySymbol.Index)
+		} else {
+			c.emit(stmt, parser.OpDefineLocal, keySymbol.Index)
+		}
+	}
+
+	// assign value variable
+	if stmt.Value.Name != "_" {
+		valueSymbol := c.symbolTable.Define(stmt.Value.Name)
+		if itSymbol.Scope == ScopeGlobal {
+			c.emit(stmt, parser.OpGetGlobal, itSymbol.Index)
+		} else {
+			c.emit(stmt, parser.OpGetLocal, itSymbol.Index)
+		}
+		c.emit(stmt, parser.OpIteratorValue)
+		if valueSymbol.Scope == ScopeGlobal {
+			c.emit(stmt, parser.OpSetGlobal, valueSymbol.Index)
+		} else {
+			c.emit(stmt, parser.OpDefineLocal, valueSymbol.Index)
+		}
+	}
+
+	// body statement
+	if err := c.Compile(stmt.Body); err != nil {
+		c.leaveLoop()
+		return err
+	}
+
+	c.leaveLoop()
+
+	// post-body position
+	postBodyPos := len(c.currentInstructions())
+
+	// back to condition
+	c.emit(stmt, parser.OpJump, preCondPos)
+
+	// post-statement position
+	postStmtPos := len(c.currentInstructions())
+	c.changeOperand(postCondPos, postStmtPos)
+
+	// update all break/continue jump positions
+	for _, pos := range loop.Breaks {
+		c.changeOperand(pos, postStmtPos)
+	}
+	for _, pos := range loop.Continues {
+		c.changeOperand(pos, postBodyPos)
+	}
+	return nil
+}
+
+func (c *Compiler) checkCyclicImports(
+	node parser.Node,
+	modulePath string,
+) error {
+	if c.modulePath == modulePath {
+		return c.errorf(node, "cyclic module import: %s", modulePath)
+	} else if c.parent != nil {
+		return c.parent.checkCyclicImports(node, modulePath)
+	}
+	return nil
+}
+
+func (c *Compiler) compileModule(
+	node parser.Node,
+	moduleName, modulePath string,
+	src []byte,
+) (*CompiledFunction, error) {
+	if err := c.checkCyclicImports(node, modulePath); err != nil {
+		return nil, err
+	}
+
+	compiledModule, exists := c.loadCompiledModule(modulePath)
+	if exists {
+		return compiledModule, nil
+	}
+
+	modFile := c.file.Set().AddFile(moduleName, -1, len(src))
+	p := parser.NewParser(modFile, src, nil)
+	file, err := p.ParseFile()
+	if err != nil {
+		return nil, err
+	}
+
+	// inherit builtin functions
+	symbolTable := NewSymbolTable()
+	for _, sym := range c.symbolTable.BuiltinSymbols() {
+		symbolTable.DefineBuiltin(sym.Index, sym.Name)
+	}
+
+	// no global scope for the module
+	symbolTable = symbolTable.Fork(false)
+
+	// compile module
+	moduleCompiler := c.fork(modFile, modulePath, symbolTable)
+	if err := moduleCompiler.Compile(file); err != nil {
+		return nil, err
+	}
+
+	// code optimization
+	moduleCompiler.optimizeFunc(node)
+	compiledFunc := moduleCompiler.Bytecode().MainFunction
+	compiledFunc.NumLocals = symbolTable.MaxSymbols()
+	c.storeCompiledModule(modulePath, compiledFunc)
+	return compiledFunc, nil
+}
+
+func (c *Compiler) loadCompiledModule(
+	modulePath string,
+) (mod *CompiledFunction, ok bool) {
+	if c.parent != nil {
+		return c.parent.loadCompiledModule(modulePath)
+	}
+	mod, ok = c.compiledModules[modulePath]
+	return
+}
+
+func (c *Compiler) storeCompiledModule(
+	modulePath string,
+	module *CompiledFunction,
+) {
+	if c.parent != nil {
+		c.parent.storeCompiledModule(modulePath, module)
+	}
+	c.compiledModules[modulePath] = module
+}
+
+func (c *Compiler) enterLoop() *loop {
+	loop := &loop{}
+	c.loops = append(c.loops, loop)
+	c.loopIndex++
+	if c.trace != nil {
+		c.printTrace("LOOPE", c.loopIndex)
+	}
+	return loop
+}
+
+func (c *Compiler) leaveLoop() {
+	if c.trace != nil {
+		c.printTrace("LOOPL", c.loopIndex)
+	}
+	c.loops = c.loops[:len(c.loops)-1]
+	c.loopIndex--
+}
+
+func (c *Compiler) currentLoop() *loop {
+	if c.loopIndex >= 0 {
+		return c.loops[c.loopIndex]
+	}
+	return nil
+}
+
+func (c *Compiler) currentInstructions() []byte {
+	return c.scopes[c.scopeIndex].Instructions
+}
+
+func (c *Compiler) currentSourceMap() map[int]parser.Pos {
+	return c.scopes[c.scopeIndex].SourceMap
+}
+
+func (c *Compiler) enterScope() {
+	scope := compilationScope{
+		SymbolInit: make(map[string]bool),
+		SourceMap:  make(map[int]parser.Pos),
+	}
+	c.scopes = append(c.scopes, scope)
+	c.scopeIndex++
+	c.symbolTable = c.symbolTable.Fork(false)
+	if c.trace != nil {
+		c.printTrace("SCOPE", c.scopeIndex)
+	}
+}
+
+func (c *Compiler) leaveScope() (
+	instructions []byte,
+	sourceMap map[int]parser.Pos,
+) {
+	instructions = c.currentInstructions()
+	sourceMap = c.currentSourceMap()
+	c.scopes = c.scopes[:len(c.scopes)-1]
+	c.scopeIndex--
+	c.symbolTable = c.symbolTable.Parent(true)
+	if c.trace != nil {
+		c.printTrace("SCOPL", c.scopeIndex)
+	}
+	return
+}
+
+func (c *Compiler) fork(
+	file *parser.SourceFile,
+	modulePath string,
+	symbolTable *SymbolTable,
+) *Compiler {
+	child := NewCompiler(file, symbolTable, nil, c.modules, c.trace)
+	child.modulePath = modulePath // module file path
+	child.parent = c              // parent to set to current compiler
+	return child
+}
+
+func (c *Compiler) error(node parser.Node, err error) error {
+	return &CompilerError{
+		FileSet: c.file.Set(),
+		Node:    node,
+		Err:     err,
+	}
+}
+
+func (c *Compiler) errorf(
+	node parser.Node,
+	format string,
+	args ...interface{},
+) error {
+	return &CompilerError{
+		FileSet: c.file.Set(),
+		Node:    node,
+		Err:     fmt.Errorf(format, args...),
+	}
+}
+
+func (c *Compiler) addConstant(o Object) int {
+	if c.parent != nil {
+		// module compilers will use their parent's constants array
+		return c.parent.addConstant(o)
+	}
+	c.constants = append(c.constants, o)
+	if c.trace != nil {
+		c.printTrace(fmt.Sprintf("CONST %04d %s", len(c.constants)-1, o))
+	}
+	return len(c.constants) - 1
+}
+
+func (c *Compiler) addInstruction(b []byte) int {
+	posNewIns := len(c.currentInstructions())
+	c.scopes[c.scopeIndex].Instructions = append(
+		c.currentInstructions(), b...)
+	return posNewIns
+}
+
+func (c *Compiler) replaceInstruction(pos int, inst []byte) {
+	copy(c.currentInstructions()[pos:], inst)
+	if c.trace != nil {
+		c.printTrace(fmt.Sprintf("REPLC %s",
+			FormatInstructions(
+				c.scopes[c.scopeIndex].Instructions[pos:], pos)[0]))
+	}
+}
+
+func (c *Compiler) changeOperand(opPos int, operand ...int) {
+	op := c.currentInstructions()[opPos]
+	inst := MakeInstruction(op, operand...)
+	c.replaceInstruction(opPos, inst)
+}
+
+// optimizeFunc performs some code-level optimization for the current function
+// instructions. It also removes unreachable (dead code) instructions and adds
+// "returns" instruction if needed.
+func (c *Compiler) optimizeFunc(node parser.Node) {
+	// any instructions between RETURN and the function end
+	// or instructions between RETURN and jump target position
+	// are considered as unreachable.
+
+	// pass 1. identify all jump destinations
+	dsts := make(map[int]bool)
+	iterateInstructions(c.scopes[c.scopeIndex].Instructions,
+		func(pos int, opcode parser.Opcode, operands []int) bool {
+			switch opcode {
+			case parser.OpJump, parser.OpJumpFalsy,
+				parser.OpAndJump, parser.OpOrJump:
+				dsts[operands[0]] = true
+			}
+			return true
+		})
+
+	// pass 2. eliminate dead code
+	var newInsts []byte
+	posMap := make(map[int]int) // old position to new position
+	var dstIdx int
+	var deadCode bool
+	iterateInstructions(c.scopes[c.scopeIndex].Instructions,
+		func(pos int, opcode parser.Opcode, operands []int) bool {
+			switch {
+			case opcode == parser.OpReturn:
+				if deadCode {
+					return true
+				}
+				deadCode = true
+			case dsts[pos]:
+				dstIdx++
+				deadCode = false
+			case deadCode:
+				return true
+			}
+			posMap[pos] = len(newInsts)
+			newInsts = append(newInsts,
+				MakeInstruction(opcode, operands...)...)
+			return true
+		})
+
+	// pass 3. update jump positions
+	var lastOp parser.Opcode
+	var appendReturn bool
+	endPos := len(c.scopes[c.scopeIndex].Instructions)
+	iterateInstructions(newInsts,
+		func(pos int, opcode parser.Opcode, operands []int) bool {
+			switch opcode {
+			case parser.OpJump, parser.OpJumpFalsy, parser.OpAndJump,
+				parser.OpOrJump:
+				newDst, ok := posMap[operands[0]]
+				if ok {
+					copy(newInsts[pos:],
+						MakeInstruction(opcode, newDst))
+				} else if endPos == operands[0] {
+					// there's a jump instruction that jumps to the end of
+					// function compiler should append "return".
+					appendReturn = true
+				} else {
+					panic(fmt.Errorf("invalid jump position: %d", newDst))
+				}
+			}
+			lastOp = opcode
+			return true
+		})
+	if lastOp != parser.OpReturn {
+		appendReturn = true
+	}
+
+	// pass 4. update source map
+	newSourceMap := make(map[int]parser.Pos)
+	for pos, srcPos := range c.scopes[c.scopeIndex].SourceMap {
+		newPos, ok := posMap[pos]
+		if ok {
+			newSourceMap[newPos] = srcPos
+		}
+	}
+	c.scopes[c.scopeIndex].Instructions = newInsts
+	c.scopes[c.scopeIndex].SourceMap = newSourceMap
+
+	// append "return"
+	if appendReturn {
+		c.emit(node, parser.OpReturn, 0)
+	}
+}
+
+func (c *Compiler) emit(
+	node parser.Node,
+	opcode parser.Opcode,
+	operands ...int,
+) int {
+	filePos := parser.NoPos
+	if node != nil {
+		filePos = node.Pos()
+	}
+
+	inst := MakeInstruction(opcode, operands...)
+	pos := c.addInstruction(inst)
+	c.scopes[c.scopeIndex].SourceMap[pos] = filePos
+	if c.trace != nil {
+		c.printTrace(fmt.Sprintf("EMIT  %s",
+			FormatInstructions(
+				c.scopes[c.scopeIndex].Instructions[pos:], pos)[0]))
+	}
+	return pos
+}
+
+func (c *Compiler) printTrace(a ...interface{}) {
+	const (
+		dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
+		n    = len(dots)
+	)
+
+	i := 2 * c.indent
+	for i > n {
+		_, _ = fmt.Fprint(c.trace, dots)
+		i -= n
+	}
+	_, _ = fmt.Fprint(c.trace, dots[0:i])
+	_, _ = fmt.Fprintln(c.trace, a...)
+}
+
+func resolveAssignLHS(
+	expr parser.Expr,
+) (name string, selectors []parser.Expr) {
+	switch term := expr.(type) {
+	case *parser.SelectorExpr:
+		name, selectors = resolveAssignLHS(term.Expr)
+		selectors = append(selectors, term.Sel)
+		return
+	case *parser.IndexExpr:
+		name, selectors = resolveAssignLHS(term.Expr)
+		selectors = append(selectors, term.Index)
+	case *parser.Ident:
+		name = term.Name
+	}
+	return
+}
+
+func iterateInstructions(
+	b []byte,
+	fn func(pos int, opcode parser.Opcode, operands []int) bool,
+) {
+	for i := 0; i < len(b); i++ {
+		numOperands := parser.OpcodeOperands[b[i]]
+		operands, read := parser.ReadOperands(numOperands, b[i+1:])
+		if !fn(i, b[i], operands) {
+			break
+		}
+		i += read
+	}
+}
+
+func tracec(c *Compiler, msg string) *Compiler {
+	c.printTrace(msg, "{")
+	c.indent++
+	return c
+}
+
+func untracec(c *Compiler) {
+	c.indent--
+	c.printTrace("}")
+}
diff --git a/vendor/github.com/d5/tengo/v2/doc.go b/vendor/github.com/d5/tengo/v2/doc.go
new file mode 100644
index 00000000..05b47de1
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/doc.go
@@ -0,0 +1,3 @@
+// tengo is a small, dynamic, fast, secure script language for Go.
+
+package tengo
diff --git a/vendor/github.com/d5/tengo/v2/errors.go b/vendor/github.com/d5/tengo/v2/errors.go
new file mode 100644
index 00000000..a3fd1f3b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/errors.go
@@ -0,0 +1,64 @@
+package tengo
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	// ErrStackOverflow is a stack overflow error.
+	ErrStackOverflow = errors.New("stack overflow")
+
+	// ErrObjectAllocLimit is an objects allocation limit error.
+	ErrObjectAllocLimit = errors.New("object allocation limit exceeded")
+
+	// ErrIndexOutOfBounds is an error where a given index is out of the
+	// bounds.
+	ErrIndexOutOfBounds = errors.New("index out of bounds")
+
+	// ErrInvalidIndexType represents an invalid index type.
+	ErrInvalidIndexType = errors.New("invalid index type")
+
+	// ErrInvalidIndexValueType represents an invalid index value type.
+	ErrInvalidIndexValueType = errors.New("invalid index value type")
+
+	// ErrInvalidIndexOnError represents an invalid index on error.
+	ErrInvalidIndexOnError = errors.New("invalid index on error")
+
+	// ErrInvalidOperator represents an error for invalid operator usage.
+	ErrInvalidOperator = errors.New("invalid operator")
+
+	// ErrWrongNumArguments represents a wrong number of arguments error.
+	ErrWrongNumArguments = errors.New("wrong number of arguments")
+
+	// ErrBytesLimit represents an error where the size of bytes value exceeds
+	// the limit.
+	ErrBytesLimit = errors.New("exceeding bytes size limit")
+
+	// ErrStringLimit represents an error where the size of string value
+	// exceeds the limit.
+	ErrStringLimit = errors.New("exceeding string size limit")
+
+	// ErrNotIndexable is an error where an Object is not indexable.
+	ErrNotIndexable = errors.New("not indexable")
+
+	// ErrNotIndexAssignable is an error where an Object is not index
+	// assignable.
+	ErrNotIndexAssignable = errors.New("not index-assignable")
+
+	// ErrNotImplemented is an error where an Object has not implemented a
+	// required method.
+	ErrNotImplemented = errors.New("not implemented")
+)
+
+// ErrInvalidArgumentType represents an invalid argument value type error.
+type ErrInvalidArgumentType struct {
+	Name     string
+	Expected string
+	Found    string
+}
+
+func (e ErrInvalidArgumentType) Error() string {
+	return fmt.Sprintf("invalid type for argument '%s': expected %s, found %s",
+		e.Name, e.Expected, e.Found)
+}
diff --git a/vendor/github.com/d5/tengo/v2/formatter.go b/vendor/github.com/d5/tengo/v2/formatter.go
new file mode 100644
index 00000000..0dbf71c6
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/formatter.go
@@ -0,0 +1,1245 @@
+package tengo
+
+import (
+	"strconv"
+	"sync"
+	"unicode/utf8"
+)
+
+// Strings for use with fmtbuf.WriteString. This is less overhead than using
+// fmtbuf.Write with byte arrays.
+const (
+	commaSpaceString  = ", "
+	nilParenString    = "(nil)"
+	percentBangString = "%!"
+	missingString     = "(MISSING)"
+	badIndexString    = "(BADINDEX)"
+	extraString       = "%!(EXTRA "
+	badWidthString    = "%!(BADWIDTH)"
+	badPrecString     = "%!(BADPREC)"
+	noVerbString      = "%!(NOVERB)"
+)
+
+const (
+	ldigits = "0123456789abcdefx"
+	udigits = "0123456789ABCDEFX"
+)
+
+const (
+	signed   = true
+	unsigned = false
+)
+
+// flags placed in a separate struct for easy clearing.
+type fmtFlags struct {
+	widPresent  bool
+	precPresent bool
+	minus       bool
+	plus        bool
+	sharp       bool
+	space       bool
+	zero        bool
+
+	// For the formats %+v %#v, we set the plusV/sharpV flags
+	// and clear the plus/sharp flags since %+v and %#v are in effect
+	// different, flagless formats set at the top level.
+	plusV  bool
+	sharpV bool
+
+	// error-related flags.
+	inDetail    bool
+	needNewline bool
+	needColon   bool
+}
+
+// A formatter is the raw formatter used by Printf etc.
+// It prints into a fmtbuf that must be set up separately.
+type formatter struct {
+	buf *fmtbuf
+
+	fmtFlags
+
+	wid  int // width
+	prec int // precision
+
+	// intbuf is large enough to store %b of an int64 with a sign and
+	// avoids padding at the end of the struct on 32 bit architectures.
+	intbuf [68]byte
+}
+
+func (f *formatter) clearFlags() {
+	f.fmtFlags = fmtFlags{}
+}
+
+func (f *formatter) init(buf *fmtbuf) {
+	f.buf = buf
+	f.clearFlags()
+}
+
+// writePadding generates n bytes of padding.
+func (f *formatter) writePadding(n int) {
+	if n <= 0 { // No padding bytes needed.
+		return
+	}
+	buf := *f.buf
+	oldLen := len(buf)
+	newLen := oldLen + n
+
+	if newLen > MaxStringLen {
+		panic(ErrStringLimit)
+	}
+
+	// Make enough room for padding.
+	if newLen > cap(buf) {
+		buf = make(fmtbuf, cap(buf)*2+n)
+		copy(buf, *f.buf)
+	}
+	// Decide which byte the padding should be filled with.
+	padByte := byte(' ')
+	if f.zero {
+		padByte = byte('0')
+	}
+	// Fill padding with padByte.
+	padding := buf[oldLen:newLen]
+	for i := range padding {
+		padding[i] = padByte
+	}
+	*f.buf = buf[:newLen]
+}
+
+// pad appends b to f.buf, padded on left (!f.minus) or right (f.minus).
+func (f *formatter) pad(b []byte) {
+	if !f.widPresent || f.wid == 0 {
+		f.buf.Write(b)
+		return
+	}
+	width := f.wid - utf8.RuneCount(b)
+	if !f.minus {
+		// left padding
+		f.writePadding(width)
+		f.buf.Write(b)
+	} else {
+		// right padding
+		f.buf.Write(b)
+		f.writePadding(width)
+	}
+}
+
+// padString appends s to f.buf, padded on left (!f.minus) or right (f.minus).
+func (f *formatter) padString(s string) {
+	if !f.widPresent || f.wid == 0 {
+		f.buf.WriteString(s)
+		return
+	}
+	width := f.wid - utf8.RuneCountInString(s)
+	if !f.minus {
+		// left padding
+		f.writePadding(width)
+		f.buf.WriteString(s)
+	} else {
+		// right padding
+		f.buf.WriteString(s)
+		f.writePadding(width)
+	}
+}
+
+// fmtBoolean formats a boolean.
+func (f *formatter) fmtBoolean(v bool) {
+	if v {
+		f.padString("true")
+	} else {
+		f.padString("false")
+	}
+}
+
+// fmtUnicode formats a uint64 as "U+0078" or with f.sharp set as "U+0078 'x'".
+func (f *formatter) fmtUnicode(u uint64) {
+	buf := f.intbuf[0:]
+
+	// With default precision set the maximum needed buf length is 18
+	// for formatting -1 with %#U ("U+FFFFFFFFFFFFFFFF") which fits
+	// into the already allocated intbuf with a capacity of 68 bytes.
+	prec := 4
+	if f.precPresent && f.prec > 4 {
+		prec = f.prec
+		// Compute space needed for "U+" , number, " '", character, "'".
+		width := 2 + prec + 2 + utf8.UTFMax + 1
+		if width > len(buf) {
+			buf = make([]byte, width)
+		}
+	}
+
+	// Format into buf, ending at buf[i]. Formatting numbers is easier
+	// right-to-left.
+	i := len(buf)
+
+	// For %#U we want to add a space and a quoted character at the end of
+	// the fmtbuf.
+	if f.sharp && u <= utf8.MaxRune && strconv.IsPrint(rune(u)) {
+		i--
+		buf[i] = '\''
+		i -= utf8.RuneLen(rune(u))
+		utf8.EncodeRune(buf[i:], rune(u))
+		i--
+		buf[i] = '\''
+		i--
+		buf[i] = ' '
+	}
+	// Format the Unicode code point u as a hexadecimal number.
+	for u >= 16 {
+		i--
+		buf[i] = udigits[u&0xF]
+		prec--
+		u >>= 4
+	}
+	i--
+	buf[i] = udigits[u]
+	prec--
+	// Add zeros in front of the number until requested precision is reached.
+	for prec > 0 {
+		i--
+		buf[i] = '0'
+		prec--
+	}
+	// Add a leading "U+".
+	i--
+	buf[i] = '+'
+	i--
+	buf[i] = 'U'
+
+	oldZero := f.zero
+	f.zero = false
+	f.pad(buf[i:])
+	f.zero = oldZero
+}
+
+// fmtInteger formats signed and unsigned integers.
+func (f *formatter) fmtInteger(
+	u uint64,
+	base int,
+	isSigned bool,
+	verb rune,
+	digits string,
+) {
+	negative := isSigned && int64(u) < 0
+	if negative {
+		u = -u
+	}
+
+	buf := f.intbuf[0:]
+	// The already allocated f.intbuf with a capacity of 68 bytes
+	// is large enough for integer formatting when no precision or width is set.
+	if f.widPresent || f.precPresent {
+		// Account 3 extra bytes for possible addition of a sign and "0x".
+		width := 3 + f.wid + f.prec // wid and prec are always positive.
+		if width > len(buf) {
+			// We're going to need a bigger boat.
+			buf = make([]byte, width)
+		}
+	}
+
+	// Two ways to ask for extra leading zero digits: %.3d or %03d.
+	// If both are specified the f.zero flag is ignored and
+	// padding with spaces is used instead.
+	prec := 0
+	if f.precPresent {
+		prec = f.prec
+		// Precision of 0 and value of 0 means "print nothing" but padding.
+		if prec == 0 && u == 0 {
+			oldZero := f.zero
+			f.zero = false
+			f.writePadding(f.wid)
+			f.zero = oldZero
+			return
+		}
+	} else if f.zero && f.widPresent {
+		prec = f.wid
+		if negative || f.plus || f.space {
+			prec-- // leave room for sign
+		}
+	}
+
+	// Because printing is easier right-to-left: format u into buf, ending at
+	// buf[i]. We could make things marginally faster by splitting the 32-bit
+	// case out into a separate block but it's not worth the duplication, so
+	// u has 64 bits.
+	i := len(buf)
+	// Use constants for the division and modulo for more efficient code.
+	// Switch cases ordered by popularity.
+	switch base {
+	case 10:
+		for u >= 10 {
+			i--
+			next := u / 10
+			buf[i] = byte('0' + u - next*10)
+			u = next
+		}
+	case 16:
+		for u >= 16 {
+			i--
+			buf[i] = digits[u&0xF]
+			u >>= 4
+		}
+	case 8:
+		for u >= 8 {
+			i--
+			buf[i] = byte('0' + u&7)
+			u >>= 3
+		}
+	case 2:
+		for u >= 2 {
+			i--
+			buf[i] = byte('0' + u&1)
+			u >>= 1
+		}
+	default:
+		panic("fmt: unknown base; can't happen")
+	}
+	i--
+	buf[i] = digits[u]
+	for i > 0 && prec > len(buf)-i {
+		i--
+		buf[i] = '0'
+	}
+
+	// Various prefixes: 0x, -, etc.
+	if f.sharp {
+		switch base {
+		case 2:
+			// Add a leading 0b.
+			i--
+			buf[i] = 'b'
+			i--
+			buf[i] = '0'
+		case 8:
+			if buf[i] != '0' {
+				i--
+				buf[i] = '0'
+			}
+		case 16:
+			// Add a leading 0x or 0X.
+			i--
+			buf[i] = digits[16]
+			i--
+			buf[i] = '0'
+		}
+	}
+	if verb == 'O' {
+		i--
+		buf[i] = 'o'
+		i--
+		buf[i] = '0'
+	}
+
+	if negative {
+		i--
+		buf[i] = '-'
+	} else if f.plus {
+		i--
+		buf[i] = '+'
+	} else if f.space {
+		i--
+		buf[i] = ' '
+	}
+
+	// Left padding with zeros has already been handled like precision earlier
+	// or the f.zero flag is ignored due to an explicitly set precision.
+	oldZero := f.zero
+	f.zero = false
+	f.pad(buf[i:])
+	f.zero = oldZero
+}
+
+// truncate truncates the string s to the specified precision, if present.
+func (f *formatter) truncateString(s string) string {
+	if f.precPresent {
+		n := f.prec
+		for i := range s {
+			n--
+			if n < 0 {
+				return s[:i]
+			}
+		}
+	}
+	return s
+}
+
+// truncate truncates the byte slice b as a string of the specified precision,
+// if present.
+func (f *formatter) truncate(b []byte) []byte {
+	if f.precPresent {
+		n := f.prec
+		for i := 0; i < len(b); {
+			n--
+			if n < 0 {
+				return b[:i]
+			}
+			wid := 1
+			if b[i] >= utf8.RuneSelf {
+				_, wid = utf8.DecodeRune(b[i:])
+			}
+			i += wid
+		}
+	}
+	return b
+}
+
+// fmtS formats a string.
+func (f *formatter) fmtS(s string) {
+	s = f.truncateString(s)
+	f.padString(s)
+}
+
+// fmtBs formats the byte slice b as if it was formatted as string with fmtS.
+func (f *formatter) fmtBs(b []byte) {
+	b = f.truncate(b)
+	f.pad(b)
+}
+
+// fmtSbx formats a string or byte slice as a hexadecimal encoding of its bytes.
+func (f *formatter) fmtSbx(s string, b []byte, digits string) {
+	length := len(b)
+	if b == nil {
+		// No byte slice present. Assume string s should be encoded.
+		length = len(s)
+	}
+	// Set length to not process more bytes than the precision demands.
+	if f.precPresent && f.prec < length {
+		length = f.prec
+	}
+	// Compute width of the encoding taking into account the f.sharp and
+	// f.space flag.
+	width := 2 * length
+	if width > 0 {
+		if f.space {
+			// Each element encoded by two hexadecimals will get a leading
+			// 0x or 0X.
+			if f.sharp {
+				width *= 2
+			}
+			// Elements will be separated by a space.
+			width += length - 1
+		} else if f.sharp {
+			// Only a leading 0x or 0X will be added for the whole string.
+			width += 2
+		}
+	} else { // The byte slice or string that should be encoded is empty.
+		if f.widPresent {
+			f.writePadding(f.wid)
+		}
+		return
+	}
+	// Handle padding to the left.
+	if f.widPresent && f.wid > width && !f.minus {
+		f.writePadding(f.wid - width)
+	}
+	// Write the encoding directly into the output fmtbuf.
+	buf := *f.buf
+	if f.sharp {
+		// Add leading 0x or 0X.
+		buf = append(buf, '0', digits[16])
+	}
+	var c byte
+	for i := 0; i < length; i++ {
+		if f.space && i > 0 {
+			// Separate elements with a space.
+			buf = append(buf, ' ')
+			if f.sharp {
+				// Add leading 0x or 0X for each element.
+				buf = append(buf, '0', digits[16])
+			}
+		}
+		if b != nil {
+			c = b[i] // Take a byte from the input byte slice.
+		} else {
+			c = s[i] // Take a byte from the input string.
+		}
+		// Encode each byte as two hexadecimal digits.
+		buf = append(buf, digits[c>>4], digits[c&0xF])
+	}
+	*f.buf = buf
+	// Handle padding to the right.
+	if f.widPresent && f.wid > width && f.minus {
+		f.writePadding(f.wid - width)
+	}
+}
+
+// fmtSx formats a string as a hexadecimal encoding of its bytes.
+func (f *formatter) fmtSx(s, digits string) {
+	f.fmtSbx(s, nil, digits)
+}
+
+// fmtBx formats a byte slice as a hexadecimal encoding of its bytes.
+func (f *formatter) fmtBx(b []byte, digits string) {
+	f.fmtSbx("", b, digits)
+}
+
+// fmtQ formats a string as a double-quoted, escaped Go string constant.
+// If f.sharp is set a raw (backquoted) string may be returned instead
+// if the string does not contain any control characters other than tab.
+func (f *formatter) fmtQ(s string) {
+	s = f.truncateString(s)
+	if f.sharp && strconv.CanBackquote(s) {
+		f.padString("`" + s + "`")
+		return
+	}
+	buf := f.intbuf[:0]
+	if f.plus {
+		f.pad(strconv.AppendQuoteToASCII(buf, s))
+	} else {
+		f.pad(strconv.AppendQuote(buf, s))
+	}
+}
+
+// fmtC formats an integer as a Unicode character.
+// If the character is not valid Unicode, it will print '\ufffd'.
+func (f *formatter) fmtC(c uint64) {
+	r := rune(c)
+	if c > utf8.MaxRune {
+		r = utf8.RuneError
+	}
+	buf := f.intbuf[:0]
+	w := utf8.EncodeRune(buf[:utf8.UTFMax], r)
+	f.pad(buf[:w])
+}
+
+// fmtQc formats an integer as a single-quoted, escaped Go character constant.
+// If the character is not valid Unicode, it will print '\ufffd'.
+func (f *formatter) fmtQc(c uint64) {
+	r := rune(c)
+	if c > utf8.MaxRune {
+		r = utf8.RuneError
+	}
+	buf := f.intbuf[:0]
+	if f.plus {
+		f.pad(strconv.AppendQuoteRuneToASCII(buf, r))
+	} else {
+		f.pad(strconv.AppendQuoteRune(buf, r))
+	}
+}
+
+// fmtFloat formats a float64. It assumes that verb is a valid format specifier
+// for strconv.AppendFloat and therefore fits into a byte.
+func (f *formatter) fmtFloat(v float64, size int, verb rune, prec int) {
+	// Explicit precision in format specifier overrules default precision.
+	if f.precPresent {
+		prec = f.prec
+	}
+	// Format number, reserving space for leading + sign if needed.
+	num := strconv.AppendFloat(f.intbuf[:1], v, byte(verb), prec, size)
+	if num[1] == '-' || num[1] == '+' {
+		num = num[1:]
+	} else {
+		num[0] = '+'
+	}
+	// f.space means to add a leading space instead of a "+" sign unless
+	// the sign is explicitly asked for by f.plus.
+	if f.space && num[0] == '+' && !f.plus {
+		num[0] = ' '
+	}
+	// Special handling for infinities and NaN,
+	// which don't look like a number so shouldn't be padded with zeros.
+	if num[1] == 'I' || num[1] == 'N' {
+		oldZero := f.zero
+		f.zero = false
+		// Remove sign before NaN if not asked for.
+		if num[1] == 'N' && !f.space && !f.plus {
+			num = num[1:]
+		}
+		f.pad(num)
+		f.zero = oldZero
+		return
+	}
+	// The sharp flag forces printing a decimal point for non-binary formats
+	// and retains trailing zeros, which we may need to restore.
+	if f.sharp && verb != 'b' {
+		digits := 0
+		switch verb {
+		case 'v', 'g', 'G', 'x':
+			digits = prec
+			// If no precision is set explicitly use a precision of 6.
+			if digits == -1 {
+				digits = 6
+			}
+		}
+
+		// Buffer pre-allocated with enough room for
+		// exponent notations of the form "e+123" or "p-1023".
+		var tailBuf [6]byte
+		tail := tailBuf[:0]
+
+		hasDecimalPoint := false
+		// Starting from i = 1 to skip sign at num[0].
+		for i := 1; i < len(num); i++ {
+			switch num[i] {
+			case '.':
+				hasDecimalPoint = true
+			case 'p', 'P':
+				tail = append(tail, num[i:]...)
+				num = num[:i]
+			case 'e', 'E':
+				if verb != 'x' && verb != 'X' {
+					tail = append(tail, num[i:]...)
+					num = num[:i]
+					break
+				}
+				fallthrough
+			default:
+				digits--
+			}
+		}
+		if !hasDecimalPoint {
+			num = append(num, '.')
+		}
+		for digits > 0 {
+			num = append(num, '0')
+			digits--
+		}
+		num = append(num, tail...)
+	}
+	// We want a sign if asked for and if the sign is not positive.
+	if f.plus || num[0] != '+' {
+		// If we're zero padding to the left we want the sign before the
+		// leading zeros. Achieve this by writing the sign out and then padding
+		// the unsigned number.
+		if f.zero && f.widPresent && f.wid > len(num) {
+			f.buf.WriteSingleByte(num[0])
+			f.writePadding(f.wid - len(num))
+			f.buf.Write(num[1:])
+			return
+		}
+		f.pad(num)
+		return
+	}
+	// No sign to show and the number is positive; just print the unsigned
+	// number.
+	f.pad(num[1:])
+}
+
+// Use simple []byte instead of bytes.Buffer to avoid large dependency.
+type fmtbuf []byte
+
+func (b *fmtbuf) Write(p []byte) {
+	if len(*b)+len(p) > MaxStringLen {
+		panic(ErrStringLimit)
+	}
+
+	*b = append(*b, p...)
+}
+
+func (b *fmtbuf) WriteString(s string) {
+	if len(*b)+len(s) > MaxStringLen {
+		panic(ErrStringLimit)
+	}
+
+	*b = append(*b, s...)
+}
+
+func (b *fmtbuf) WriteSingleByte(c byte) {
+	if len(*b) >= MaxStringLen {
+		panic(ErrStringLimit)
+	}
+
+	*b = append(*b, c)
+}
+
+func (b *fmtbuf) WriteRune(r rune) {
+	if len(*b)+utf8.RuneLen(r) > MaxStringLen {
+		panic(ErrStringLimit)
+	}
+
+	if r < utf8.RuneSelf {
+		*b = append(*b, byte(r))
+		return
+	}
+
+	b2 := *b
+	n := len(b2)
+	for n+utf8.UTFMax > cap(b2) {
+		b2 = append(b2, 0)
+	}
+	w := utf8.EncodeRune(b2[n:n+utf8.UTFMax], r)
+	*b = b2[:n+w]
+}
+
+// pp is used to store a printer's state and is reused with sync.Pool to avoid
+// allocations.
+type pp struct {
+	buf fmtbuf
+
+	// arg holds the current item.
+	arg Object
+
+	// fmt is used to format basic items such as integers or strings.
+	fmt formatter
+
+	// reordered records whether the format string used argument reordering.
+	reordered bool
+
+	// goodArgNum records whether the most recent reordering directive was
+	// valid.
+	goodArgNum bool
+
+	// erroring is set when printing an error string to guard against calling
+	// handleMethods.
+	erroring bool
+}
+
+var ppFree = sync.Pool{
+	New: func() interface{} { return new(pp) },
+}
+
+// newPrinter allocates a new pp struct or grabs a cached one.
+func newPrinter() *pp {
+	p := ppFree.Get().(*pp)
+	p.erroring = false
+	p.fmt.init(&p.buf)
+	return p
+}
+
+// free saves used pp structs in ppFree; avoids an allocation per invocation.
+func (p *pp) free() {
+	// Proper usage of a sync.Pool requires each entry to have approximately
+	// the same memory cost. To obtain this property when the stored type
+	// contains a variably-sized fmtbuf, we add a hard limit on the maximum
+	// fmtbuf to place back in the pool.
+	//
+	// See https://golang.org/issue/23199
+	if cap(p.buf) > 64<<10 {
+		return
+	}
+
+	p.buf = p.buf[:0]
+	p.arg = nil
+	ppFree.Put(p)
+}
+
+func (p *pp) Width() (wid int, ok bool) {
+	return p.fmt.wid, p.fmt.widPresent
+}
+
+func (p *pp) Precision() (prec int, ok bool) {
+	return p.fmt.prec, p.fmt.precPresent
+}
+
+func (p *pp) Flag(b int) bool {
+	switch b {
+	case '-':
+		return p.fmt.minus
+	case '+':
+		return p.fmt.plus || p.fmt.plusV
+	case '#':
+		return p.fmt.sharp || p.fmt.sharpV
+	case ' ':
+		return p.fmt.space
+	case '0':
+		return p.fmt.zero
+	}
+	return false
+}
+
+// Implement Write so we can call Fprintf on a pp (through State), for
+// recursive use in custom verbs.
+func (p *pp) Write(b []byte) (ret int, err error) {
+	p.buf.Write(b)
+	return len(b), nil
+}
+
+// Implement WriteString so that we can call io.WriteString
+// on a pp (through state), for efficiency.
+func (p *pp) WriteString(s string) (ret int, err error) {
+	p.buf.WriteString(s)
+	return len(s), nil
+}
+
+func (p *pp) WriteRune(r rune) (ret int, err error) {
+	p.buf.WriteRune(r)
+	return utf8.RuneLen(r), nil
+}
+
+func (p *pp) WriteSingleByte(c byte) (ret int, err error) {
+	p.buf.WriteSingleByte(c)
+	return 1, nil
+}
+
+// tooLarge reports whether the magnitude of the integer is
+// too large to be used as a formatting width or precision.
+func tooLarge(x int) bool {
+	const max int = 1e6
+	return x > max || x < -max
+}
+
+// parsenum converts ASCII to integer.  num is 0 (and isnum is false) if no
+// number present.
+func parsenum(s string, start, end int) (num int, isnum bool, newi int) {
+	if start >= end {
+		return 0, false, end
+	}
+	for newi = start; newi < end && '0' <= s[newi] && s[newi] <= '9'; newi++ {
+		if tooLarge(num) {
+			return 0, false, end // Overflow; crazy long number most likely.
+		}
+		num = num*10 + int(s[newi]-'0')
+		isnum = true
+	}
+	return
+}
+
+func (p *pp) badVerb(verb rune) {
+	p.erroring = true
+	_, _ = p.WriteString(percentBangString)
+	_, _ = p.WriteRune(verb)
+	_, _ = p.WriteSingleByte('(')
+	switch {
+	case p.arg != nil:
+		_, _ = p.WriteString(p.arg.String())
+		_, _ = p.WriteSingleByte('=')
+		p.printArg(p.arg, 'v')
+	default:
+		_, _ = p.WriteString(UndefinedValue.String())
+	}
+	_, _ = p.WriteSingleByte(')')
+	p.erroring = false
+}
+
+func (p *pp) fmtBool(v bool, verb rune) {
+	switch verb {
+	case 't', 'v':
+		p.fmt.fmtBoolean(v)
+	default:
+		p.badVerb(verb)
+	}
+}
+
+// fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x or
+// not, as requested, by temporarily setting the sharp flag.
+func (p *pp) fmt0x64(v uint64, leading0x bool) {
+	sharp := p.fmt.sharp
+	p.fmt.sharp = leading0x
+	p.fmt.fmtInteger(v, 16, unsigned, 'v', ldigits)
+	p.fmt.sharp = sharp
+}
+
+// fmtInteger formats a signed or unsigned integer.
+func (p *pp) fmtInteger(v uint64, isSigned bool, verb rune) {
+	switch verb {
+	case 'v':
+		if p.fmt.sharpV && !isSigned {
+			p.fmt0x64(v, true)
+		} else {
+			p.fmt.fmtInteger(v, 10, isSigned, verb, ldigits)
+		}
+	case 'd':
+		p.fmt.fmtInteger(v, 10, isSigned, verb, ldigits)
+	case 'b':
+		p.fmt.fmtInteger(v, 2, isSigned, verb, ldigits)
+	case 'o', 'O':
+		p.fmt.fmtInteger(v, 8, isSigned, verb, ldigits)
+	case 'x':
+		p.fmt.fmtInteger(v, 16, isSigned, verb, ldigits)
+	case 'X':
+		p.fmt.fmtInteger(v, 16, isSigned, verb, udigits)
+	case 'c':
+		p.fmt.fmtC(v)
+	case 'q':
+		if v <= utf8.MaxRune {
+			p.fmt.fmtQc(v)
+		} else {
+			p.badVerb(verb)
+		}
+	case 'U':
+		p.fmt.fmtUnicode(v)
+	default:
+		p.badVerb(verb)
+	}
+}
+
+// fmtFloat formats a float. The default precision for each verb
+// is specified as last argument in the call to fmt_float.
+func (p *pp) fmtFloat(v float64, size int, verb rune) {
+	switch verb {
+	case 'v':
+		p.fmt.fmtFloat(v, size, 'g', -1)
+	case 'b', 'g', 'G', 'x', 'X':
+		p.fmt.fmtFloat(v, size, verb, -1)
+	case 'f', 'e', 'E':
+		p.fmt.fmtFloat(v, size, verb, 6)
+	case 'F':
+		p.fmt.fmtFloat(v, size, 'f', 6)
+	default:
+		p.badVerb(verb)
+	}
+}
+
+func (p *pp) fmtString(v string, verb rune) {
+	switch verb {
+	case 'v':
+		if p.fmt.sharpV {
+			p.fmt.fmtQ(v)
+		} else {
+			p.fmt.fmtS(v)
+		}
+	case 's':
+		p.fmt.fmtS(v)
+	case 'x':
+		p.fmt.fmtSx(v, ldigits)
+	case 'X':
+		p.fmt.fmtSx(v, udigits)
+	case 'q':
+		p.fmt.fmtQ(v)
+	default:
+		p.badVerb(verb)
+	}
+}
+
+func (p *pp) fmtBytes(v []byte, verb rune, typeString string) {
+	switch verb {
+	case 'v', 'd':
+		if p.fmt.sharpV {
+			_, _ = p.WriteString(typeString)
+			if v == nil {
+				_, _ = p.WriteString(nilParenString)
+				return
+			}
+			_, _ = p.WriteSingleByte('{')
+			for i, c := range v {
+				if i > 0 {
+					_, _ = p.WriteString(commaSpaceString)
+				}
+				p.fmt0x64(uint64(c), true)
+			}
+			_, _ = p.WriteSingleByte('}')
+		} else {
+			_, _ = p.WriteSingleByte('[')
+			for i, c := range v {
+				if i > 0 {
+					_, _ = p.WriteSingleByte(' ')
+				}
+				p.fmt.fmtInteger(uint64(c), 10, unsigned, verb, ldigits)
+			}
+			_, _ = p.WriteSingleByte(']')
+		}
+	case 's':
+		p.fmt.fmtBs(v)
+	case 'x':
+		p.fmt.fmtBx(v, ldigits)
+	case 'X':
+		p.fmt.fmtBx(v, udigits)
+	case 'q':
+		p.fmt.fmtQ(string(v))
+	}
+}
+
+func (p *pp) printArg(arg Object, verb rune) {
+	p.arg = arg
+
+	if arg == nil {
+		arg = UndefinedValue
+	}
+
+	// Special processing considerations.
+	// %T (the value's type) and %p (its address) are special; we always do
+	// them first.
+	switch verb {
+	case 'T':
+		p.fmt.fmtS(arg.TypeName())
+		return
+	case 'v':
+		p.fmt.fmtS(arg.String())
+		return
+	}
+
+	// Some types can be done without reflection.
+	switch f := arg.(type) {
+	case *Bool:
+		p.fmtBool(!f.IsFalsy(), verb)
+	case *Float:
+		p.fmtFloat(f.Value, 64, verb)
+	case *Int:
+		p.fmtInteger(uint64(f.Value), signed, verb)
+	case *String:
+		p.fmtString(f.Value, verb)
+	case *Bytes:
+		p.fmtBytes(f.Value, verb, "[]byte")
+	default:
+		p.fmtString(f.String(), verb)
+	}
+}
+
+// intFromArg gets the argNumth element of a. On return, isInt reports whether
+// the argument has integer type.
+func intFromArg(a []Object, argNum int) (num int, isInt bool, newArgNum int) {
+	newArgNum = argNum
+	if argNum < len(a) {
+		var num64 int64
+		num64, isInt = ToInt64(a[argNum])
+		num = int(num64)
+		newArgNum = argNum + 1
+		if tooLarge(num) {
+			num = 0
+			isInt = false
+		}
+	}
+	return
+}
+
+// parseArgNumber returns the value of the bracketed number, minus 1
+// (explicit argument numbers are one-indexed but we want zero-indexed).
+// The opening bracket is known to be present at format[0].
+// The returned values are the index, the number of bytes to consume
+// up to the closing paren, if present, and whether the number parsed
+// ok. The bytes to consume will be 1 if no closing paren is present.
+func parseArgNumber(format string) (index int, wid int, ok bool) {
+	// There must be at least 3 bytes: [n].
+	if len(format) < 3 {
+		return 0, 1, false
+	}
+
+	// Find closing bracket.
+	for i := 1; i < len(format); i++ {
+		if format[i] == ']' {
+			width, ok, newi := parsenum(format, 1, i)
+			if !ok || newi != i {
+				return 0, i + 1, false
+			}
+			// arg numbers are one-indexed andskip paren.
+			return width - 1, i + 1, true
+		}
+	}
+	return 0, 1, false
+}
+
+// argNumber returns the next argument to evaluate, which is either the value
+// of the passed-in argNum or the value of the bracketed integer that begins
+// format[i:]. It also returns the new value of i, that is, the index of the
+// next byte of the format to process.
+func (p *pp) argNumber(
+	argNum int,
+	format string,
+	i int,
+	numArgs int,
+) (newArgNum, newi int, found bool) {
+	if len(format) <= i || format[i] != '[' {
+		return argNum, i, false
+	}
+	p.reordered = true
+	index, wid, ok := parseArgNumber(format[i:])
+	if ok && 0 <= index && index < numArgs {
+		return index, i + wid, true
+	}
+	p.goodArgNum = false
+	return argNum, i + wid, ok
+}
+
+func (p *pp) badArgNum(verb rune) {
+	_, _ = p.WriteString(percentBangString)
+	_, _ = p.WriteRune(verb)
+	_, _ = p.WriteString(badIndexString)
+}
+
+func (p *pp) missingArg(verb rune) {
+	_, _ = p.WriteString(percentBangString)
+	_, _ = p.WriteRune(verb)
+	_, _ = p.WriteString(missingString)
+}
+
+func (p *pp) doFormat(format string, a []Object) (err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			if e, ok := r.(error); ok && e == ErrStringLimit {
+				err = e
+				return
+			}
+			panic(r)
+		}
+	}()
+
+	end := len(format)
+	argNum := 0         // we process one argument per non-trivial format
+	afterIndex := false // previous item in format was an index like [3].
+	p.reordered = false
+formatLoop:
+	for i := 0; i < end; {
+		p.goodArgNum = true
+		lasti := i
+		for i < end && format[i] != '%' {
+			i++
+		}
+		if i > lasti {
+			_, _ = p.WriteString(format[lasti:i])
+		}
+		if i >= end {
+			// done processing format string
+			break
+		}
+
+		// Process one verb
+		i++
+
+		// Do we have flags?
+		p.fmt.clearFlags()
+	simpleFormat:
+		for ; i < end; i++ {
+			c := format[i]
+			switch c {
+			case '#':
+				p.fmt.sharp = true
+			case '0':
+				// Only allow zero padding to the left.
+				p.fmt.zero = !p.fmt.minus
+			case '+':
+				p.fmt.plus = true
+			case '-':
+				p.fmt.minus = true
+				p.fmt.zero = false // Do not pad with zeros to the right.
+			case ' ':
+				p.fmt.space = true
+			default:
+				// Fast path for common case of ascii lower case simple verbs
+				// without precision or width or argument indices.
+				if 'a' <= c && c <= 'z' && argNum < len(a) {
+					if c == 'v' {
+						// Go syntax
+						p.fmt.sharpV = p.fmt.sharp
+						p.fmt.sharp = false
+						// Struct-field syntax
+						p.fmt.plusV = p.fmt.plus
+						p.fmt.plus = false
+					}
+					p.printArg(a[argNum], rune(c))
+					argNum++
+					i++
+					continue formatLoop
+				}
+				// Format is more complex than simple flags and a verb or is
+				// malformed.
+				break simpleFormat
+			}
+		}
+
+		// Do we have an explicit argument index?
+		argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
+
+		// Do we have width?
+		if i < end && format[i] == '*' {
+			i++
+			p.fmt.wid, p.fmt.widPresent, argNum = intFromArg(a, argNum)
+
+			if !p.fmt.widPresent {
+				_, _ = p.WriteString(badWidthString)
+			}
+
+			// We have a negative width, so take its value and ensure
+			// that the minus flag is set
+			if p.fmt.wid < 0 {
+				p.fmt.wid = -p.fmt.wid
+				p.fmt.minus = true
+				p.fmt.zero = false // Do not pad with zeros to the right.
+			}
+			afterIndex = false
+		} else {
+			p.fmt.wid, p.fmt.widPresent, i = parsenum(format, i, end)
+			if afterIndex && p.fmt.widPresent { // "%[3]2d"
+				p.goodArgNum = false
+			}
+		}
+
+		// Do we have precision?
+		if i+1 < end && format[i] == '.' {
+			i++
+			if afterIndex { // "%[3].2d"
+				p.goodArgNum = false
+			}
+			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
+			if i < end && format[i] == '*' {
+				i++
+				p.fmt.prec, p.fmt.precPresent, argNum = intFromArg(a, argNum)
+				// Negative precision arguments don't make sense
+				if p.fmt.prec < 0 {
+					p.fmt.prec = 0
+					p.fmt.precPresent = false
+				}
+				if !p.fmt.precPresent {
+					_, _ = p.WriteString(badPrecString)
+				}
+				afterIndex = false
+			} else {
+				p.fmt.prec, p.fmt.precPresent, i = parsenum(format, i, end)
+				if !p.fmt.precPresent {
+					p.fmt.prec = 0
+					p.fmt.precPresent = true
+				}
+			}
+		}
+
+		if !afterIndex {
+			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
+		}
+
+		if i >= end {
+			_, _ = p.WriteString(noVerbString)
+			break
+		}
+
+		verb, size := rune(format[i]), 1
+		if verb >= utf8.RuneSelf {
+			verb, size = utf8.DecodeRuneInString(format[i:])
+		}
+		i += size
+
+		switch {
+		case verb == '%':
+			// Percent does not absorb operands and ignores f.wid and f.prec.
+			_, _ = p.WriteSingleByte('%')
+		case !p.goodArgNum:
+			p.badArgNum(verb)
+		case argNum >= len(a):
+			// No argument left over to print for the current verb.
+			p.missingArg(verb)
+		case verb == 'v':
+			// Go syntax
+			p.fmt.sharpV = p.fmt.sharp
+			p.fmt.sharp = false
+			// Struct-field syntax
+			p.fmt.plusV = p.fmt.plus
+			p.fmt.plus = false
+			fallthrough
+		default:
+			p.printArg(a[argNum], verb)
+			argNum++
+		}
+	}
+
+	// Check for extra arguments unless the call accessed the arguments
+	// out of order, in which case it's too expensive to detect if they've all
+	// been used and arguably OK if they're not.
+	if !p.reordered && argNum < len(a) {
+		p.fmt.clearFlags()
+		_, _ = p.WriteString(extraString)
+		for i, arg := range a[argNum:] {
+			if i > 0 {
+				_, _ = p.WriteString(commaSpaceString)
+			}
+			if arg == nil {
+				_, _ = p.WriteString(UndefinedValue.String())
+			} else {
+				_, _ = p.WriteString(arg.TypeName())
+				_, _ = p.WriteSingleByte('=')
+				p.printArg(arg, 'v')
+			}
+		}
+		_, _ = p.WriteSingleByte(')')
+	}
+
+	return nil
+}
+
+// Format is like fmt.Sprintf but using Objects.
+func Format(format string, a ...Object) (string, error) {
+	p := newPrinter()
+	err := p.doFormat(format, a)
+	s := string(p.buf)
+	p.free()
+
+	return s, err
+}
diff --git a/vendor/github.com/d5/tengo/v2/go.mod b/vendor/github.com/d5/tengo/v2/go.mod
new file mode 100644
index 00000000..732ff142
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/go.mod
@@ -0,0 +1,3 @@
+module github.com/d5/tengo/v2
+
+go 1.13
diff --git a/vendor/github.com/d5/tengo/v2/go.sum b/vendor/github.com/d5/tengo/v2/go.sum
new file mode 100644
index 00000000..e69de29b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/go.sum
diff --git a/vendor/github.com/d5/tengo/v2/instructions.go b/vendor/github.com/d5/tengo/v2/instructions.go
new file mode 100644
index 00000000..eb1fbf27
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/instructions.go
@@ -0,0 +1,61 @@
+package tengo
+
+import (
+	"fmt"
+
+	"github.com/d5/tengo/v2/parser"
+)
+
+// MakeInstruction returns a bytecode for an opcode and the operands.
+func MakeInstruction(opcode parser.Opcode, operands ...int) []byte {
+	numOperands := parser.OpcodeOperands[opcode]
+
+	totalLen := 1
+	for _, w := range numOperands {
+		totalLen += w
+	}
+
+	instruction := make([]byte, totalLen)
+	instruction[0] = opcode
+
+	offset := 1
+	for i, o := range operands {
+		width := numOperands[i]
+		switch width {
+		case 1:
+			instruction[offset] = byte(o)
+		case 2:
+			n := uint16(o)
+			instruction[offset] = byte(n >> 8)
+			instruction[offset+1] = byte(n)
+		}
+		offset += width
+	}
+	return instruction
+}
+
+// FormatInstructions returns string representation of bytecode instructions.
+func FormatInstructions(b []byte, posOffset int) []string {
+	var out []string
+
+	i := 0
+	for i < len(b) {
+		numOperands := parser.OpcodeOperands[b[i]]
+		operands, read := parser.ReadOperands(numOperands, b[i+1:])
+
+		switch len(numOperands) {
+		case 0:
+			out = append(out, fmt.Sprintf("%04d %-7s",
+				posOffset+i, parser.OpcodeNames[b[i]]))
+		case 1:
+			out = append(out, fmt.Sprintf("%04d %-7s %-5d",
+				posOffset+i, parser.OpcodeNames[b[i]], operands[0]))
+		case 2:
+			out = append(out, fmt.Sprintf("%04d %-7s %-5d %-5d",
+				posOffset+i, parser.OpcodeNames[b[i]],
+				operands[0], operands[1]))
+		}
+		i += 1 + read
+	}
+	return out
+}
diff --git a/vendor/github.com/d5/tengo/v2/iterator.go b/vendor/github.com/d5/tengo/v2/iterator.go
new file mode 100644
index 00000000..13adbbab
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/iterator.go
@@ -0,0 +1,209 @@
+package tengo
+
+// Iterator represents an iterator for underlying data type.
+type Iterator interface {
+	Object
+
+	// Next returns true if there are more elements to iterate.
+	Next() bool
+
+	// Key returns the key or index value of the current element.
+	Key() Object
+
+	// Value returns the value of the current element.
+	Value() Object
+}
+
+// ArrayIterator is an iterator for an array.
+type ArrayIterator struct {
+	ObjectImpl
+	v []Object
+	i int
+	l int
+}
+
+// TypeName returns the name of the type.
+func (i *ArrayIterator) TypeName() string {
+	return "array-iterator"
+}
+
+func (i *ArrayIterator) String() string {
+	return "<array-iterator>"
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (i *ArrayIterator) IsFalsy() bool {
+	return true
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (i *ArrayIterator) Equals(Object) bool {
+	return false
+}
+
+// Copy returns a copy of the type.
+func (i *ArrayIterator) Copy() Object {
+	return &ArrayIterator{v: i.v, i: i.i, l: i.l}
+}
+
+// Next returns true if there are more elements to iterate.
+func (i *ArrayIterator) Next() bool {
+	i.i++
+	return i.i <= i.l
+}
+
+// Key returns the key or index value of the current element.
+func (i *ArrayIterator) Key() Object {
+	return &Int{Value: int64(i.i - 1)}
+}
+
+// Value returns the value of the current element.
+func (i *ArrayIterator) Value() Object {
+	return i.v[i.i-1]
+}
+
+// BytesIterator represents an iterator for a string.
+type BytesIterator struct {
+	ObjectImpl
+	v []byte
+	i int
+	l int
+}
+
+// TypeName returns the name of the type.
+func (i *BytesIterator) TypeName() string {
+	return "bytes-iterator"
+}
+
+func (i *BytesIterator) String() string {
+	return "<bytes-iterator>"
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (i *BytesIterator) Equals(Object) bool {
+	return false
+}
+
+// Copy returns a copy of the type.
+func (i *BytesIterator) Copy() Object {
+	return &BytesIterator{v: i.v, i: i.i, l: i.l}
+}
+
+// Next returns true if there are more elements to iterate.
+func (i *BytesIterator) Next() bool {
+	i.i++
+	return i.i <= i.l
+}
+
+// Key returns the key or index value of the current element.
+func (i *BytesIterator) Key() Object {
+	return &Int{Value: int64(i.i - 1)}
+}
+
+// Value returns the value of the current element.
+func (i *BytesIterator) Value() Object {
+	return &Int{Value: int64(i.v[i.i-1])}
+}
+
+// MapIterator represents an iterator for the map.
+type MapIterator struct {
+	ObjectImpl
+	v map[string]Object
+	k []string
+	i int
+	l int
+}
+
+// TypeName returns the name of the type.
+func (i *MapIterator) TypeName() string {
+	return "map-iterator"
+}
+
+func (i *MapIterator) String() string {
+	return "<map-iterator>"
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (i *MapIterator) IsFalsy() bool {
+	return true
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (i *MapIterator) Equals(Object) bool {
+	return false
+}
+
+// Copy returns a copy of the type.
+func (i *MapIterator) Copy() Object {
+	return &MapIterator{v: i.v, k: i.k, i: i.i, l: i.l}
+}
+
+// Next returns true if there are more elements to iterate.
+func (i *MapIterator) Next() bool {
+	i.i++
+	return i.i <= i.l
+}
+
+// Key returns the key or index value of the current element.
+func (i *MapIterator) Key() Object {
+	k := i.k[i.i-1]
+	return &String{Value: k}
+}
+
+// Value returns the value of the current element.
+func (i *MapIterator) Value() Object {
+	k := i.k[i.i-1]
+	return i.v[k]
+}
+
+// StringIterator represents an iterator for a string.
+type StringIterator struct {
+	ObjectImpl
+	v []rune
+	i int
+	l int
+}
+
+// TypeName returns the name of the type.
+func (i *StringIterator) TypeName() string {
+	return "string-iterator"
+}
+
+func (i *StringIterator) String() string {
+	return "<string-iterator>"
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (i *StringIterator) IsFalsy() bool {
+	return true
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (i *StringIterator) Equals(Object) bool {
+	return false
+}
+
+// Copy returns a copy of the type.
+func (i *StringIterator) Copy() Object {
+	return &StringIterator{v: i.v, i: i.i, l: i.l}
+}
+
+// Next returns true if there are more elements to iterate.
+func (i *StringIterator) Next() bool {
+	i.i++
+	return i.i <= i.l
+}
+
+// Key returns the key or index value of the current element.
+func (i *StringIterator) Key() Object {
+	return &Int{Value: int64(i.i - 1)}
+}
+
+// Value returns the value of the current element.
+func (i *StringIterator) Value() Object {
+	return &Char{Value: i.v[i.i-1]}
+}
diff --git a/vendor/github.com/d5/tengo/v2/modules.go b/vendor/github.com/d5/tengo/v2/modules.go
new file mode 100644
index 00000000..c8fcde7f
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/modules.go
@@ -0,0 +1,93 @@
+package tengo
+
+// Importable interface represents importable module instance.
+type Importable interface {
+	// Import should return either an Object or module source code ([]byte).
+	Import(moduleName string) (interface{}, error)
+}
+
+// ModuleMap represents a set of named modules. Use NewModuleMap to create a
+// new module map.
+type ModuleMap struct {
+	m map[string]Importable
+}
+
+// NewModuleMap creates a new module map.
+func NewModuleMap() *ModuleMap {
+	return &ModuleMap{
+		m: make(map[string]Importable),
+	}
+}
+
+// Add adds an import module.
+func (m *ModuleMap) Add(name string, module Importable) {
+	m.m[name] = module
+}
+
+// AddBuiltinModule adds a builtin module.
+func (m *ModuleMap) AddBuiltinModule(name string, attrs map[string]Object) {
+	m.m[name] = &BuiltinModule{Attrs: attrs}
+}
+
+// AddSourceModule adds a source module.
+func (m *ModuleMap) AddSourceModule(name string, src []byte) {
+	m.m[name] = &SourceModule{Src: src}
+}
+
+// Remove removes a named module.
+func (m *ModuleMap) Remove(name string) {
+	delete(m.m, name)
+}
+
+// Get returns an import module identified by name. It returns if the name is
+// not found.
+func (m *ModuleMap) Get(name string) Importable {
+	return m.m[name]
+}
+
+// GetBuiltinModule returns a builtin module identified by name. It returns
+// if the name is not found or the module is not a builtin module.
+func (m *ModuleMap) GetBuiltinModule(name string) *BuiltinModule {
+	mod, _ := m.m[name].(*BuiltinModule)
+	return mod
+}
+
+// GetSourceModule returns a source module identified by name. It returns if
+// the name is not found or the module is not a source module.
+func (m *ModuleMap) GetSourceModule(name string) *SourceModule {
+	mod, _ := m.m[name].(*SourceModule)
+	return mod
+}
+
+// Copy creates a copy of the module map.
+func (m *ModuleMap) Copy() *ModuleMap {
+	c := &ModuleMap{
+		m: make(map[string]Importable),
+	}
+	for name, mod := range m.m {
+		c.m[name] = mod
+	}
+	return c
+}
+
+// Len returns the number of named modules.
+func (m *ModuleMap) Len() int {
+	return len(m.m)
+}
+
+// AddMap adds named modules from another module map.
+func (m *ModuleMap) AddMap(o *ModuleMap) {
+	for name, mod := range o.m {
+		m.m[name] = mod
+	}
+}
+
+// SourceModule is an importable module that's written in Tengo.
+type SourceModule struct {
+	Src []byte
+}
+
+// Import returns a module source code.
+func (m *SourceModule) Import(_ string) (interface{}, error) {
+	return m.Src, nil
+}
diff --git a/vendor/github.com/d5/tengo/v2/objects.go b/vendor/github.com/d5/tengo/v2/objects.go
new file mode 100644
index 00000000..27c1d493
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/objects.go
@@ -0,0 +1,1581 @@
+package tengo
+
+import (
+	"bytes"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/d5/tengo/v2/parser"
+	"github.com/d5/tengo/v2/token"
+)
+
+var (
+	// TrueValue represents a true value.
+	TrueValue Object = &Bool{value: true}
+
+	// FalseValue represents a false value.
+	FalseValue Object = &Bool{value: false}
+
+	// UndefinedValue represents an undefined value.
+	UndefinedValue Object = &Undefined{}
+)
+
+// Object represents an object in the VM.
+type Object interface {
+	// TypeName should return the name of the type.
+	TypeName() string
+
+	// String should return a string representation of the type's value.
+	String() string
+
+	// BinaryOp should return another object that is the result of a given
+	// binary operator and a right-hand side object. If BinaryOp returns an
+	// error, the VM will treat it as a run-time error.
+	BinaryOp(op token.Token, rhs Object) (Object, error)
+
+	// IsFalsy should return true if the value of the type should be considered
+	// as falsy.
+	IsFalsy() bool
+
+	// Equals should return true if the value of the type should be considered
+	// as equal to the value of another object.
+	Equals(another Object) bool
+
+	// Copy should return a copy of the type (and its value). Copy function
+	// will be used for copy() builtin function which is expected to deep-copy
+	// the values generally.
+	Copy() Object
+
+	// IndexGet should take an index Object and return a result Object or an
+	// error for indexable objects. Indexable is an object that can take an
+	// index and return an object. If error is returned, the runtime will treat
+	// it as a run-time error and ignore returned value. If Object is not
+	// indexable, ErrNotIndexable should be returned as error. If nil is
+	// returned as value, it will be converted to UndefinedToken value by the
+	// runtime.
+	IndexGet(index Object) (value Object, err error)
+
+	// IndexSet should take an index Object and a value Object for index
+	// assignable objects. Index assignable is an object that can take an index
+	// and a value on the left-hand side of the assignment statement. If Object
+	// is not index assignable, ErrNotIndexAssignable should be returned as
+	// error. If an error is returned, it will be treated as a run-time error.
+	IndexSet(index, value Object) error
+
+	// Iterate should return an Iterator for the type.
+	Iterate() Iterator
+
+	// CanIterate should return whether the Object can be Iterated.
+	CanIterate() bool
+
+	// Call should take an arbitrary number of arguments and returns a return
+	// value and/or an error, which the VM will consider as a run-time error.
+	Call(args ...Object) (ret Object, err error)
+
+	// CanCall should return whether the Object can be Called.
+	CanCall() bool
+}
+
+// ObjectImpl represents a default Object Implementation. To defined a new
+// value type, one can embed ObjectImpl in their type declarations to avoid
+// implementing all non-significant methods. TypeName() and String() methods
+// still need to be implemented.
+type ObjectImpl struct {
+}
+
+// TypeName returns the name of the type.
+func (o *ObjectImpl) TypeName() string {
+	panic(ErrNotImplemented)
+}
+
+func (o *ObjectImpl) String() string {
+	panic(ErrNotImplemented)
+}
+
+// BinaryOp returns another object that is the result of a given binary
+// operator and a right-hand side object.
+func (o *ObjectImpl) BinaryOp(_ token.Token, _ Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *ObjectImpl) Copy() Object {
+	return nil
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *ObjectImpl) IsFalsy() bool {
+	return false
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *ObjectImpl) Equals(x Object) bool {
+	return o == x
+}
+
+// IndexGet returns an element at a given index.
+func (o *ObjectImpl) IndexGet(_ Object) (res Object, err error) {
+	return nil, ErrNotIndexable
+}
+
+// IndexSet sets an element at a given index.
+func (o *ObjectImpl) IndexSet(_, _ Object) (err error) {
+	return ErrNotIndexAssignable
+}
+
+// Iterate returns an iterator.
+func (o *ObjectImpl) Iterate() Iterator {
+	return nil
+}
+
+// CanIterate returns whether the Object can be Iterated.
+func (o *ObjectImpl) CanIterate() bool {
+	return false
+}
+
+// Call takes an arbitrary number of arguments and returns a return value
+// and/or an error.
+func (o *ObjectImpl) Call(_ ...Object) (ret Object, err error) {
+	return nil, nil
+}
+
+// CanCall returns whether the Object can be Called.
+func (o *ObjectImpl) CanCall() bool {
+	return false
+}
+
+// Array represents an array of objects.
+type Array struct {
+	ObjectImpl
+	Value []Object
+}
+
+// TypeName returns the name of the type.
+func (o *Array) TypeName() string {
+	return "array"
+}
+
+func (o *Array) String() string {
+	var elements []string
+	for _, e := range o.Value {
+		elements = append(elements, e.String())
+	}
+	return fmt.Sprintf("[%s]", strings.Join(elements, ", "))
+}
+
+// BinaryOp returns another object that is the result of a given binary
+// operator and a right-hand side object.
+func (o *Array) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	if rhs, ok := rhs.(*Array); ok {
+		switch op {
+		case token.Add:
+			if len(rhs.Value) == 0 {
+				return o, nil
+			}
+			return &Array{Value: append(o.Value, rhs.Value...)}, nil
+		}
+	}
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Array) Copy() Object {
+	var c []Object
+	for _, elem := range o.Value {
+		c = append(c, elem.Copy())
+	}
+	return &Array{Value: c}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Array) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Array) Equals(x Object) bool {
+	var xVal []Object
+	switch x := x.(type) {
+	case *Array:
+		xVal = x.Value
+	case *ImmutableArray:
+		xVal = x.Value
+	default:
+		return false
+	}
+	if len(o.Value) != len(xVal) {
+		return false
+	}
+	for i, e := range o.Value {
+		if !e.Equals(xVal[i]) {
+			return false
+		}
+	}
+	return true
+}
+
+// IndexGet returns an element at a given index.
+func (o *Array) IndexGet(index Object) (res Object, err error) {
+	intIdx, ok := index.(*Int)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+	idxVal := int(intIdx.Value)
+	if idxVal < 0 || idxVal >= len(o.Value) {
+		res = UndefinedValue
+		return
+	}
+	res = o.Value[idxVal]
+	return
+}
+
+// IndexSet sets an element at a given index.
+func (o *Array) IndexSet(index, value Object) (err error) {
+	intIdx, ok := ToInt(index)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+	if intIdx < 0 || intIdx >= len(o.Value) {
+		err = ErrIndexOutOfBounds
+		return
+	}
+	o.Value[intIdx] = value
+	return nil
+}
+
+// Iterate creates an array iterator.
+func (o *Array) Iterate() Iterator {
+	return &ArrayIterator{
+		v: o.Value,
+		l: len(o.Value),
+	}
+}
+
+// CanIterate returns whether the Object can be Iterated.
+func (o *Array) CanIterate() bool {
+	return true
+}
+
+// Bool represents a boolean value.
+type Bool struct {
+	ObjectImpl
+
+	// this is intentionally non-public to force using objects.TrueValue and
+	// FalseValue always
+	value bool
+}
+
+func (o *Bool) String() string {
+	if o.value {
+		return "true"
+	}
+
+	return "false"
+}
+
+// TypeName returns the name of the type.
+func (o *Bool) TypeName() string {
+	return "bool"
+}
+
+// Copy returns a copy of the type.
+func (o *Bool) Copy() Object {
+	return o
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Bool) IsFalsy() bool {
+	return !o.value
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Bool) Equals(x Object) bool {
+	return o == x
+}
+
+// GobDecode decodes bool value from input bytes.
+func (o *Bool) GobDecode(b []byte) (err error) {
+	o.value = b[0] == 1
+	return
+}
+
+// GobEncode encodes bool values into bytes.
+func (o *Bool) GobEncode() (b []byte, err error) {
+	if o.value {
+		b = []byte{1}
+	} else {
+		b = []byte{0}
+	}
+	return
+}
+
+// BuiltinFunction represents a builtin function.
+type BuiltinFunction struct {
+	ObjectImpl
+	Name  string
+	Value CallableFunc
+}
+
+// TypeName returns the name of the type.
+func (o *BuiltinFunction) TypeName() string {
+	return "builtin-function:" + o.Name
+}
+
+func (o *BuiltinFunction) String() string {
+	return "<builtin-function>"
+}
+
+// Copy returns a copy of the type.
+func (o *BuiltinFunction) Copy() Object {
+	return &BuiltinFunction{Value: o.Value}
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *BuiltinFunction) Equals(_ Object) bool {
+	return false
+}
+
+// Call executes a builtin function.
+func (o *BuiltinFunction) Call(args ...Object) (Object, error) {
+	return o.Value(args...)
+}
+
+// CanCall returns whether the Object can be Called.
+func (o *BuiltinFunction) CanCall() bool {
+	return true
+}
+
+// BuiltinModule is an importable module that's written in Go.
+type BuiltinModule struct {
+	Attrs map[string]Object
+}
+
+// Import returns an immutable map for the module.
+func (m *BuiltinModule) Import(moduleName string) (interface{}, error) {
+	return m.AsImmutableMap(moduleName), nil
+}
+
+// AsImmutableMap converts builtin module into an immutable map.
+func (m *BuiltinModule) AsImmutableMap(moduleName string) *ImmutableMap {
+	attrs := make(map[string]Object, len(m.Attrs))
+	for k, v := range m.Attrs {
+		attrs[k] = v.Copy()
+	}
+	attrs["__module_name__"] = &String{Value: moduleName}
+	return &ImmutableMap{Value: attrs}
+}
+
+// Bytes represents a byte array.
+type Bytes struct {
+	ObjectImpl
+	Value []byte
+}
+
+func (o *Bytes) String() string {
+	return string(o.Value)
+}
+
+// TypeName returns the name of the type.
+func (o *Bytes) TypeName() string {
+	return "bytes"
+}
+
+// BinaryOp returns another object that is the result of a given binary
+// operator and a right-hand side object.
+func (o *Bytes) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch op {
+	case token.Add:
+		switch rhs := rhs.(type) {
+		case *Bytes:
+			if len(o.Value)+len(rhs.Value) > MaxBytesLen {
+				return nil, ErrBytesLimit
+			}
+			return &Bytes{Value: append(o.Value, rhs.Value...)}, nil
+		}
+	}
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Bytes) Copy() Object {
+	return &Bytes{Value: append([]byte{}, o.Value...)}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Bytes) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Bytes) Equals(x Object) bool {
+	t, ok := x.(*Bytes)
+	if !ok {
+		return false
+	}
+	return bytes.Equal(o.Value, t.Value)
+}
+
+// IndexGet returns an element (as Int) at a given index.
+func (o *Bytes) IndexGet(index Object) (res Object, err error) {
+	intIdx, ok := index.(*Int)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+	idxVal := int(intIdx.Value)
+	if idxVal < 0 || idxVal >= len(o.Value) {
+		res = UndefinedValue
+		return
+	}
+	res = &Int{Value: int64(o.Value[idxVal])}
+	return
+}
+
+// Iterate creates a bytes iterator.
+func (o *Bytes) Iterate() Iterator {
+	return &BytesIterator{
+		v: o.Value,
+		l: len(o.Value),
+	}
+}
+
+// CanIterate returns whether the Object can be Iterated.
+func (o *Bytes) CanIterate() bool {
+	return true
+}
+
+// Char represents a character value.
+type Char struct {
+	ObjectImpl
+	Value rune
+}
+
+func (o *Char) String() string {
+	return string(o.Value)
+}
+
+// TypeName returns the name of the type.
+func (o *Char) TypeName() string {
+	return "char"
+}
+
+// BinaryOp returns another object that is the result of a given binary
+// operator and a right-hand side object.
+func (o *Char) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch rhs := rhs.(type) {
+	case *Char:
+		switch op {
+		case token.Add:
+			r := o.Value + rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Char{Value: r}, nil
+		case token.Sub:
+			r := o.Value - rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Char{Value: r}, nil
+		case token.Less:
+			if o.Value < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	case *Int:
+		switch op {
+		case token.Add:
+			r := o.Value + rune(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Char{Value: r}, nil
+		case token.Sub:
+			r := o.Value - rune(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Char{Value: r}, nil
+		case token.Less:
+			if int64(o.Value) < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if int64(o.Value) > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if int64(o.Value) <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if int64(o.Value) >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	}
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Char) Copy() Object {
+	return &Char{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Char) IsFalsy() bool {
+	return o.Value == 0
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Char) Equals(x Object) bool {
+	t, ok := x.(*Char)
+	if !ok {
+		return false
+	}
+	return o.Value == t.Value
+}
+
+// CompiledFunction represents a compiled function.
+type CompiledFunction struct {
+	ObjectImpl
+	Instructions  []byte
+	NumLocals     int // number of local variables (including function parameters)
+	NumParameters int
+	VarArgs       bool
+	SourceMap     map[int]parser.Pos
+	Free          []*ObjectPtr
+}
+
+// TypeName returns the name of the type.
+func (o *CompiledFunction) TypeName() string {
+	return "compiled-function"
+}
+
+func (o *CompiledFunction) String() string {
+	return "<compiled-function>"
+}
+
+// Copy returns a copy of the type.
+func (o *CompiledFunction) Copy() Object {
+	return &CompiledFunction{
+		Instructions:  append([]byte{}, o.Instructions...),
+		NumLocals:     o.NumLocals,
+		NumParameters: o.NumParameters,
+		VarArgs:       o.VarArgs,
+		Free:          append([]*ObjectPtr{}, o.Free...), // DO NOT Copy() of elements; these are variable pointers
+	}
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *CompiledFunction) Equals(_ Object) bool {
+	return false
+}
+
+// SourcePos returns the source position of the instruction at ip.
+func (o *CompiledFunction) SourcePos(ip int) parser.Pos {
+	for ip >= 0 {
+		if p, ok := o.SourceMap[ip]; ok {
+			return p
+		}
+		ip--
+	}
+	return parser.NoPos
+}
+
+// CanCall returns whether the Object can be Called.
+func (o *CompiledFunction) CanCall() bool {
+	return true
+}
+
+// Error represents an error value.
+type Error struct {
+	ObjectImpl
+	Value Object
+}
+
+// TypeName returns the name of the type.
+func (o *Error) TypeName() string {
+	return "error"
+}
+
+func (o *Error) String() string {
+	if o.Value != nil {
+		return fmt.Sprintf("error: %s", o.Value.String())
+	}
+	return "error"
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Error) IsFalsy() bool {
+	return true // error is always false.
+}
+
+// Copy returns a copy of the type.
+func (o *Error) Copy() Object {
+	return &Error{Value: o.Value.Copy()}
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Error) Equals(x Object) bool {
+	return o == x // pointer equality
+}
+
+// IndexGet returns an element at a given index.
+func (o *Error) IndexGet(index Object) (res Object, err error) {
+	if strIdx, _ := ToString(index); strIdx != "value" {
+		err = ErrInvalidIndexOnError
+		return
+	}
+	res = o.Value
+	return
+}
+
+// Float represents a floating point number value.
+type Float struct {
+	ObjectImpl
+	Value float64
+}
+
+func (o *Float) String() string {
+	return strconv.FormatFloat(o.Value, 'f', -1, 64)
+}
+
+// TypeName returns the name of the type.
+func (o *Float) TypeName() string {
+	return "float"
+}
+
+// BinaryOp returns another object that is the result of a given binary
+// operator and a right-hand side object.
+func (o *Float) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch rhs := rhs.(type) {
+	case *Float:
+		switch op {
+		case token.Add:
+			r := o.Value + rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Sub:
+			r := o.Value - rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Mul:
+			r := o.Value * rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Quo:
+			r := o.Value / rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Less:
+			if o.Value < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	case *Int:
+		switch op {
+		case token.Add:
+			r := o.Value + float64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Sub:
+			r := o.Value - float64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Mul:
+			r := o.Value * float64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Quo:
+			r := o.Value / float64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Float{Value: r}, nil
+		case token.Less:
+			if o.Value < float64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > float64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= float64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= float64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	}
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Float) Copy() Object {
+	return &Float{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Float) IsFalsy() bool {
+	return math.IsNaN(o.Value)
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Float) Equals(x Object) bool {
+	t, ok := x.(*Float)
+	if !ok {
+		return false
+	}
+	return o.Value == t.Value
+}
+
+// ImmutableArray represents an immutable array of objects.
+type ImmutableArray struct {
+	ObjectImpl
+	Value []Object
+}
+
+// TypeName returns the name of the type.
+func (o *ImmutableArray) TypeName() string {
+	return "immutable-array"
+}
+
+func (o *ImmutableArray) String() string {
+	var elements []string
+	for _, e := range o.Value {
+		elements = append(elements, e.String())
+	}
+	return fmt.Sprintf("[%s]", strings.Join(elements, ", "))
+}
+
+// BinaryOp returns another object that is the result of a given binary
+// operator and a right-hand side object.
+func (o *ImmutableArray) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	if rhs, ok := rhs.(*ImmutableArray); ok {
+		switch op {
+		case token.Add:
+			return &Array{Value: append(o.Value, rhs.Value...)}, nil
+		}
+	}
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *ImmutableArray) Copy() Object {
+	var c []Object
+	for _, elem := range o.Value {
+		c = append(c, elem.Copy())
+	}
+	return &Array{Value: c}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *ImmutableArray) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *ImmutableArray) Equals(x Object) bool {
+	var xVal []Object
+	switch x := x.(type) {
+	case *Array:
+		xVal = x.Value
+	case *ImmutableArray:
+		xVal = x.Value
+	default:
+		return false
+	}
+	if len(o.Value) != len(xVal) {
+		return false
+	}
+	for i, e := range o.Value {
+		if !e.Equals(xVal[i]) {
+			return false
+		}
+	}
+	return true
+}
+
+// IndexGet returns an element at a given index.
+func (o *ImmutableArray) IndexGet(index Object) (res Object, err error) {
+	intIdx, ok := index.(*Int)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+	idxVal := int(intIdx.Value)
+	if idxVal < 0 || idxVal >= len(o.Value) {
+		res = UndefinedValue
+		return
+	}
+	res = o.Value[idxVal]
+	return
+}
+
+// Iterate creates an array iterator.
+func (o *ImmutableArray) Iterate() Iterator {
+	return &ArrayIterator{
+		v: o.Value,
+		l: len(o.Value),
+	}
+}
+
+// CanIterate returns whether the Object can be Iterated.
+func (o *ImmutableArray) CanIterate() bool {
+	return true
+}
+
+// ImmutableMap represents an immutable map object.
+type ImmutableMap struct {
+	ObjectImpl
+	Value map[string]Object
+}
+
+// TypeName returns the name of the type.
+func (o *ImmutableMap) TypeName() string {
+	return "immutable-map"
+}
+
+func (o *ImmutableMap) String() string {
+	var pairs []string
+	for k, v := range o.Value {
+		pairs = append(pairs, fmt.Sprintf("%s: %s", k, v.String()))
+	}
+	return fmt.Sprintf("{%s}", strings.Join(pairs, ", "))
+}
+
+// Copy returns a copy of the type.
+func (o *ImmutableMap) Copy() Object {
+	c := make(map[string]Object)
+	for k, v := range o.Value {
+		c[k] = v.Copy()
+	}
+	return &Map{Value: c}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *ImmutableMap) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// IndexGet returns the value for the given key.
+func (o *ImmutableMap) IndexGet(index Object) (res Object, err error) {
+	strIdx, ok := ToString(index)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+	res, ok = o.Value[strIdx]
+	if !ok {
+		res = UndefinedValue
+	}
+	return
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *ImmutableMap) Equals(x Object) bool {
+	var xVal map[string]Object
+	switch x := x.(type) {
+	case *Map:
+		xVal = x.Value
+	case *ImmutableMap:
+		xVal = x.Value
+	default:
+		return false
+	}
+	if len(o.Value) != len(xVal) {
+		return false
+	}
+	for k, v := range o.Value {
+		tv := xVal[k]
+		if !v.Equals(tv) {
+			return false
+		}
+	}
+	return true
+}
+
+// Iterate creates an immutable map iterator.
+func (o *ImmutableMap) Iterate() Iterator {
+	var keys []string
+	for k := range o.Value {
+		keys = append(keys, k)
+	}
+	return &MapIterator{
+		v: o.Value,
+		k: keys,
+		l: len(keys),
+	}
+}
+
+// CanIterate returns whether the Object can be Iterated.
+func (o *ImmutableMap) CanIterate() bool {
+	return true
+}
+
+// Int represents an integer value.
+type Int struct {
+	ObjectImpl
+	Value int64
+}
+
+func (o *Int) String() string {
+	return strconv.FormatInt(o.Value, 10)
+}
+
+// TypeName returns the name of the type.
+func (o *Int) TypeName() string {
+	return "int"
+}
+
+// BinaryOp returns another object that is the result of a given binary
+// operator and a right-hand side object.
+func (o *Int) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch rhs := rhs.(type) {
+	case *Int:
+		switch op {
+		case token.Add:
+			r := o.Value + rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Sub:
+			r := o.Value - rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Mul:
+			r := o.Value * rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Quo:
+			r := o.Value / rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Rem:
+			r := o.Value % rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.And:
+			r := o.Value & rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Or:
+			r := o.Value | rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Xor:
+			r := o.Value ^ rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.AndNot:
+			r := o.Value &^ rhs.Value
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Shl:
+			r := o.Value << uint64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Shr:
+			r := o.Value >> uint64(rhs.Value)
+			if r == o.Value {
+				return o, nil
+			}
+			return &Int{Value: r}, nil
+		case token.Less:
+			if o.Value < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	case *Float:
+		switch op {
+		case token.Add:
+			return &Float{Value: float64(o.Value) + rhs.Value}, nil
+		case token.Sub:
+			return &Float{Value: float64(o.Value) - rhs.Value}, nil
+		case token.Mul:
+			return &Float{Value: float64(o.Value) * rhs.Value}, nil
+		case token.Quo:
+			return &Float{Value: float64(o.Value) / rhs.Value}, nil
+		case token.Less:
+			if float64(o.Value) < rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if float64(o.Value) > rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if float64(o.Value) <= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if float64(o.Value) >= rhs.Value {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	case *Char:
+		switch op {
+		case token.Add:
+			return &Char{Value: rune(o.Value) + rhs.Value}, nil
+		case token.Sub:
+			return &Char{Value: rune(o.Value) - rhs.Value}, nil
+		case token.Less:
+			if o.Value < int64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value > int64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value <= int64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value >= int64(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	}
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Int) Copy() Object {
+	return &Int{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Int) IsFalsy() bool {
+	return o.Value == 0
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Int) Equals(x Object) bool {
+	t, ok := x.(*Int)
+	if !ok {
+		return false
+	}
+	return o.Value == t.Value
+}
+
+// Map represents a map of objects.
+type Map struct {
+	ObjectImpl
+	Value map[string]Object
+}
+
+// TypeName returns the name of the type.
+func (o *Map) TypeName() string {
+	return "map"
+}
+
+func (o *Map) String() string {
+	var pairs []string
+	for k, v := range o.Value {
+		pairs = append(pairs, fmt.Sprintf("%s: %s", k, v.String()))
+	}
+	return fmt.Sprintf("{%s}", strings.Join(pairs, ", "))
+}
+
+// Copy returns a copy of the type.
+func (o *Map) Copy() Object {
+	c := make(map[string]Object)
+	for k, v := range o.Value {
+		c[k] = v.Copy()
+	}
+	return &Map{Value: c}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Map) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Map) Equals(x Object) bool {
+	var xVal map[string]Object
+	switch x := x.(type) {
+	case *Map:
+		xVal = x.Value
+	case *ImmutableMap:
+		xVal = x.Value
+	default:
+		return false
+	}
+	if len(o.Value) != len(xVal) {
+		return false
+	}
+	for k, v := range o.Value {
+		tv := xVal[k]
+		if !v.Equals(tv) {
+			return false
+		}
+	}
+	return true
+}
+
+// IndexGet returns the value for the given key.
+func (o *Map) IndexGet(index Object) (res Object, err error) {
+	strIdx, ok := ToString(index)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+	res, ok = o.Value[strIdx]
+	if !ok {
+		res = UndefinedValue
+	}
+	return
+}
+
+// IndexSet sets the value for the given key.
+func (o *Map) IndexSet(index, value Object) (err error) {
+	strIdx, ok := ToString(index)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+	o.Value[strIdx] = value
+	return nil
+}
+
+// Iterate creates a map iterator.
+func (o *Map) Iterate() Iterator {
+	var keys []string
+	for k := range o.Value {
+		keys = append(keys, k)
+	}
+	return &MapIterator{
+		v: o.Value,
+		k: keys,
+		l: len(keys),
+	}
+}
+
+// CanIterate returns whether the Object can be Iterated.
+func (o *Map) CanIterate() bool {
+	return true
+}
+
+// ObjectPtr represents a free variable.
+type ObjectPtr struct {
+	ObjectImpl
+	Value *Object
+}
+
+func (o *ObjectPtr) String() string {
+	return "free-var"
+}
+
+// TypeName returns the name of the type.
+func (o *ObjectPtr) TypeName() string {
+	return "<free-var>"
+}
+
+// Copy returns a copy of the type.
+func (o *ObjectPtr) Copy() Object {
+	return o
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *ObjectPtr) IsFalsy() bool {
+	return o.Value == nil
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *ObjectPtr) Equals(x Object) bool {
+	return o == x
+}
+
+// String represents a string value.
+type String struct {
+	ObjectImpl
+	Value   string
+	runeStr []rune
+}
+
+// TypeName returns the name of the type.
+func (o *String) TypeName() string {
+	return "string"
+}
+
+func (o *String) String() string {
+	return strconv.Quote(o.Value)
+}
+
+// BinaryOp returns another object that is the result of a given binary
+// operator and a right-hand side object.
+func (o *String) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch op {
+	case token.Add:
+		switch rhs := rhs.(type) {
+		case *String:
+			if len(o.Value)+len(rhs.Value) > MaxStringLen {
+				return nil, ErrStringLimit
+			}
+			return &String{Value: o.Value + rhs.Value}, nil
+		default:
+			rhsStr := rhs.String()
+			if len(o.Value)+len(rhsStr) > MaxStringLen {
+				return nil, ErrStringLimit
+			}
+			return &String{Value: o.Value + rhsStr}, nil
+		}
+	}
+	return nil, ErrInvalidOperator
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *String) IsFalsy() bool {
+	return len(o.Value) == 0
+}
+
+// Copy returns a copy of the type.
+func (o *String) Copy() Object {
+	return &String{Value: o.Value}
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *String) Equals(x Object) bool {
+	t, ok := x.(*String)
+	if !ok {
+		return false
+	}
+	return o.Value == t.Value
+}
+
+// IndexGet returns a character at a given index.
+func (o *String) IndexGet(index Object) (res Object, err error) {
+	intIdx, ok := index.(*Int)
+	if !ok {
+		err = ErrInvalidIndexType
+		return
+	}
+	idxVal := int(intIdx.Value)
+	if o.runeStr == nil {
+		o.runeStr = []rune(o.Value)
+	}
+	if idxVal < 0 || idxVal >= len(o.runeStr) {
+		res = UndefinedValue
+		return
+	}
+	res = &Char{Value: o.runeStr[idxVal]}
+	return
+}
+
+// Iterate creates a string iterator.
+func (o *String) Iterate() Iterator {
+	if o.runeStr == nil {
+		o.runeStr = []rune(o.Value)
+	}
+	return &StringIterator{
+		v: o.runeStr,
+		l: len(o.runeStr),
+	}
+}
+
+// CanIterate returns whether the Object can be Iterated.
+func (o *String) CanIterate() bool {
+	return true
+}
+
+// Time represents a time value.
+type Time struct {
+	ObjectImpl
+	Value time.Time
+}
+
+func (o *Time) String() string {
+	return o.Value.String()
+}
+
+// TypeName returns the name of the type.
+func (o *Time) TypeName() string {
+	return "time"
+}
+
+// BinaryOp returns another object that is the result of a given binary
+// operator and a right-hand side object.
+func (o *Time) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	switch rhs := rhs.(type) {
+	case *Int:
+		switch op {
+		case token.Add: // time + int => time
+			if rhs.Value == 0 {
+				return o, nil
+			}
+			return &Time{Value: o.Value.Add(time.Duration(rhs.Value))}, nil
+		case token.Sub: // time - int => time
+			if rhs.Value == 0 {
+				return o, nil
+			}
+			return &Time{Value: o.Value.Add(time.Duration(-rhs.Value))}, nil
+		}
+	case *Time:
+		switch op {
+		case token.Sub: // time - time => int (duration)
+			return &Int{Value: int64(o.Value.Sub(rhs.Value))}, nil
+		case token.Less: // time < time => bool
+			if o.Value.Before(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.Greater:
+			if o.Value.After(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.LessEq:
+			if o.Value.Equal(rhs.Value) || o.Value.Before(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		case token.GreaterEq:
+			if o.Value.Equal(rhs.Value) || o.Value.After(rhs.Value) {
+				return TrueValue, nil
+			}
+			return FalseValue, nil
+		}
+	}
+	return nil, ErrInvalidOperator
+}
+
+// Copy returns a copy of the type.
+func (o *Time) Copy() Object {
+	return &Time{Value: o.Value}
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Time) IsFalsy() bool {
+	return o.Value.IsZero()
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Time) Equals(x Object) bool {
+	t, ok := x.(*Time)
+	if !ok {
+		return false
+	}
+	return o.Value.Equal(t.Value)
+}
+
+// Undefined represents an undefined value.
+type Undefined struct {
+	ObjectImpl
+}
+
+// TypeName returns the name of the type.
+func (o *Undefined) TypeName() string {
+	return "undefined"
+}
+
+func (o *Undefined) String() string {
+	return "<undefined>"
+}
+
+// Copy returns a copy of the type.
+func (o *Undefined) Copy() Object {
+	return o
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (o *Undefined) IsFalsy() bool {
+	return true
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *Undefined) Equals(x Object) bool {
+	return o == x
+}
+
+// IndexGet returns an element at a given index.
+func (o *Undefined) IndexGet(_ Object) (Object, error) {
+	return UndefinedValue, nil
+}
+
+// Iterate creates a map iterator.
+func (o *Undefined) Iterate() Iterator {
+	return o
+}
+
+// CanIterate returns whether the Object can be Iterated.
+func (o *Undefined) CanIterate() bool {
+	return true
+}
+
+// Next returns true if there are more elements to iterate.
+func (o *Undefined) Next() bool {
+	return false
+}
+
+// Key returns the key or index value of the current element.
+func (o *Undefined) Key() Object {
+	return o
+}
+
+// Value returns the value of the current element.
+func (o *Undefined) Value() Object {
+	return o
+}
+
+// UserFunction represents a user function.
+type UserFunction struct {
+	ObjectImpl
+	Name       string
+	Value      CallableFunc
+	EncodingID string
+}
+
+// TypeName returns the name of the type.
+func (o *UserFunction) TypeName() string {
+	return "user-function:" + o.Name
+}
+
+func (o *UserFunction) String() string {
+	return "<user-function>"
+}
+
+// Copy returns a copy of the type.
+func (o *UserFunction) Copy() Object {
+	return &UserFunction{Value: o.Value}
+}
+
+// Equals returns true if the value of the type is equal to the value of
+// another object.
+func (o *UserFunction) Equals(_ Object) bool {
+	return false
+}
+
+// Call invokes a user function.
+func (o *UserFunction) Call(args ...Object) (Object, error) {
+	return o.Value(args...)
+}
+
+// CanCall returns whether the Object can be Called.
+func (o *UserFunction) CanCall() bool {
+	return true
+}
diff --git a/vendor/github.com/d5/tengo/v2/parser/ast.go b/vendor/github.com/d5/tengo/v2/parser/ast.go
new file mode 100644
index 00000000..8c2f7c07
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/parser/ast.go
@@ -0,0 +1,69 @@
+package parser
+
+import (
+	"strings"
+)
+
+const (
+	nullRep = "<null>"
+)
+
+// Node represents a node in the AST.
+type Node interface {
+	// Pos returns the position of first character belonging to the node.
+	Pos() Pos
+	// End returns the position of first character immediately after the node.
+	End() Pos
+	// String returns a string representation of the node.
+	String() string
+}
+
+// IdentList represents a list of identifiers.
+type IdentList struct {
+	LParen  Pos
+	VarArgs bool
+	List    []*Ident
+	RParen  Pos
+}
+
+// Pos returns the position of first character belonging to the node.
+func (n *IdentList) Pos() Pos {
+	if n.LParen.IsValid() {
+		return n.LParen
+	}
+	if len(n.List) > 0 {
+		return n.List[0].Pos()
+	}
+	return NoPos
+}
+
+// End returns the position of first character immediately after the node.
+func (n *IdentList) End() Pos {
+	if n.RParen.IsValid() {
+		return n.RParen + 1
+	}
+	if l := len(n.List); l > 0 {
+		return n.List[l-1].End()
+	}
+	return NoPos
+}
+
+// NumFields returns the number of fields.
+func (n *IdentList) NumFields() int {
+	if n == nil {
+		return 0
+	}
+	return len(n.List)
+}
+
+func (n *IdentList) String() string {
+	var list []string
+	for i, e := range n.List {
+		if n.VarArgs && i == len(n.List)-1 {
+			list = append(list, "..."+e.String())
+		} else {
+			list = append(list, e.String())
+		}
+	}
+	return "(" + strings.Join(list, ", ") + ")"
+}
diff --git a/vendor/github.com/d5/tengo/v2/parser/expr.go b/vendor/github.com/d5/tengo/v2/parser/expr.go
new file mode 100644
index 00000000..71e5155b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/parser/expr.go
@@ -0,0 +1,597 @@
+package parser
+
+import (
+	"strings"
+
+	"github.com/d5/tengo/v2/token"
+)
+
+// Expr represents an expression node in the AST.
+type Expr interface {
+	Node
+	exprNode()
+}
+
+// ArrayLit represents an array literal.
+type ArrayLit struct {
+	Elements []Expr
+	LBrack   Pos
+	RBrack   Pos
+}
+
+func (e *ArrayLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ArrayLit) Pos() Pos {
+	return e.LBrack
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ArrayLit) End() Pos {
+	return e.RBrack + 1
+}
+
+func (e *ArrayLit) String() string {
+	var elements []string
+	for _, m := range e.Elements {
+		elements = append(elements, m.String())
+	}
+	return "[" + strings.Join(elements, ", ") + "]"
+}
+
+// BadExpr represents a bad expression.
+type BadExpr struct {
+	From Pos
+	To   Pos
+}
+
+func (e *BadExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *BadExpr) Pos() Pos {
+	return e.From
+}
+
+// End returns the position of first character immediately after the node.
+func (e *BadExpr) End() Pos {
+	return e.To
+}
+
+func (e *BadExpr) String() string {
+	return "<bad expression>"
+}
+
+// BinaryExpr represents a binary operator expression.
+type BinaryExpr struct {
+	LHS      Expr
+	RHS      Expr
+	Token    token.Token
+	TokenPos Pos
+}
+
+func (e *BinaryExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *BinaryExpr) Pos() Pos {
+	return e.LHS.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *BinaryExpr) End() Pos {
+	return e.RHS.End()
+}
+
+func (e *BinaryExpr) String() string {
+	return "(" + e.LHS.String() + " " + e.Token.String() +
+		" " + e.RHS.String() + ")"
+}
+
+// BoolLit represents a boolean literal.
+type BoolLit struct {
+	Value    bool
+	ValuePos Pos
+	Literal  string
+}
+
+func (e *BoolLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *BoolLit) Pos() Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *BoolLit) End() Pos {
+	return Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *BoolLit) String() string {
+	return e.Literal
+}
+
+// CallExpr represents a function call expression.
+type CallExpr struct {
+	Func   Expr
+	LParen Pos
+	Args   []Expr
+	RParen Pos
+}
+
+func (e *CallExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *CallExpr) Pos() Pos {
+	return e.Func.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *CallExpr) End() Pos {
+	return e.RParen + 1
+}
+
+func (e *CallExpr) String() string {
+	var args []string
+	for _, e := range e.Args {
+		args = append(args, e.String())
+	}
+	return e.Func.String() + "(" + strings.Join(args, ", ") + ")"
+}
+
+// CharLit represents a character literal.
+type CharLit struct {
+	Value    rune
+	ValuePos Pos
+	Literal  string
+}
+
+func (e *CharLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *CharLit) Pos() Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *CharLit) End() Pos {
+	return Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *CharLit) String() string {
+	return e.Literal
+}
+
+// CondExpr represents a ternary conditional expression.
+type CondExpr struct {
+	Cond        Expr
+	True        Expr
+	False       Expr
+	QuestionPos Pos
+	ColonPos    Pos
+}
+
+func (e *CondExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *CondExpr) Pos() Pos {
+	return e.Cond.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *CondExpr) End() Pos {
+	return e.False.End()
+}
+
+func (e *CondExpr) String() string {
+	return "(" + e.Cond.String() + " ? " + e.True.String() +
+		" : " + e.False.String() + ")"
+}
+
+// ErrorExpr represents an error expression
+type ErrorExpr struct {
+	Expr     Expr
+	ErrorPos Pos
+	LParen   Pos
+	RParen   Pos
+}
+
+func (e *ErrorExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ErrorExpr) Pos() Pos {
+	return e.ErrorPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ErrorExpr) End() Pos {
+	return e.RParen
+}
+
+func (e *ErrorExpr) String() string {
+	return "error(" + e.Expr.String() + ")"
+}
+
+// FloatLit represents a floating point literal.
+type FloatLit struct {
+	Value    float64
+	ValuePos Pos
+	Literal  string
+}
+
+func (e *FloatLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *FloatLit) Pos() Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *FloatLit) End() Pos {
+	return Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *FloatLit) String() string {
+	return e.Literal
+}
+
+// FuncLit represents a function literal.
+type FuncLit struct {
+	Type *FuncType
+	Body *BlockStmt
+}
+
+func (e *FuncLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *FuncLit) Pos() Pos {
+	return e.Type.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *FuncLit) End() Pos {
+	return e.Body.End()
+}
+
+func (e *FuncLit) String() string {
+	return "func" + e.Type.Params.String() + " " + e.Body.String()
+}
+
+// FuncType represents a function type definition.
+type FuncType struct {
+	FuncPos Pos
+	Params  *IdentList
+}
+
+func (e *FuncType) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *FuncType) Pos() Pos {
+	return e.FuncPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *FuncType) End() Pos {
+	return e.Params.End()
+}
+
+func (e *FuncType) String() string {
+	return "func" + e.Params.String()
+}
+
+// Ident represents an identifier.
+type Ident struct {
+	Name    string
+	NamePos Pos
+}
+
+func (e *Ident) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *Ident) Pos() Pos {
+	return e.NamePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *Ident) End() Pos {
+	return Pos(int(e.NamePos) + len(e.Name))
+}
+
+func (e *Ident) String() string {
+	if e != nil {
+		return e.Name
+	}
+	return nullRep
+}
+
+// ImmutableExpr represents an immutable expression
+type ImmutableExpr struct {
+	Expr     Expr
+	ErrorPos Pos
+	LParen   Pos
+	RParen   Pos
+}
+
+func (e *ImmutableExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ImmutableExpr) Pos() Pos {
+	return e.ErrorPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ImmutableExpr) End() Pos {
+	return e.RParen
+}
+
+func (e *ImmutableExpr) String() string {
+	return "immutable(" + e.Expr.String() + ")"
+}
+
+// ImportExpr represents an import expression
+type ImportExpr struct {
+	ModuleName string
+	Token      token.Token
+	TokenPos   Pos
+}
+
+func (e *ImportExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ImportExpr) Pos() Pos {
+	return e.TokenPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ImportExpr) End() Pos {
+	// import("moduleName")
+	return Pos(int(e.TokenPos) + 10 + len(e.ModuleName))
+}
+
+func (e *ImportExpr) String() string {
+	return `import("` + e.ModuleName + `")"`
+}
+
+// IndexExpr represents an index expression.
+type IndexExpr struct {
+	Expr   Expr
+	LBrack Pos
+	Index  Expr
+	RBrack Pos
+}
+
+func (e *IndexExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *IndexExpr) Pos() Pos {
+	return e.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *IndexExpr) End() Pos {
+	return e.RBrack + 1
+}
+
+func (e *IndexExpr) String() string {
+	var index string
+	if e.Index != nil {
+		index = e.Index.String()
+	}
+	return e.Expr.String() + "[" + index + "]"
+}
+
+// IntLit represents an integer literal.
+type IntLit struct {
+	Value    int64
+	ValuePos Pos
+	Literal  string
+}
+
+func (e *IntLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *IntLit) Pos() Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *IntLit) End() Pos {
+	return Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *IntLit) String() string {
+	return e.Literal
+}
+
+// MapElementLit represents a map element.
+type MapElementLit struct {
+	Key      string
+	KeyPos   Pos
+	ColonPos Pos
+	Value    Expr
+}
+
+func (e *MapElementLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *MapElementLit) Pos() Pos {
+	return e.KeyPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *MapElementLit) End() Pos {
+	return e.Value.End()
+}
+
+func (e *MapElementLit) String() string {
+	return e.Key + ": " + e.Value.String()
+}
+
+// MapLit represents a map literal.
+type MapLit struct {
+	LBrace   Pos
+	Elements []*MapElementLit
+	RBrace   Pos
+}
+
+func (e *MapLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *MapLit) Pos() Pos {
+	return e.LBrace
+}
+
+// End returns the position of first character immediately after the node.
+func (e *MapLit) End() Pos {
+	return e.RBrace + 1
+}
+
+func (e *MapLit) String() string {
+	var elements []string
+	for _, m := range e.Elements {
+		elements = append(elements, m.String())
+	}
+	return "{" + strings.Join(elements, ", ") + "}"
+}
+
+// ParenExpr represents a parenthesis wrapped expression.
+type ParenExpr struct {
+	Expr   Expr
+	LParen Pos
+	RParen Pos
+}
+
+func (e *ParenExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ParenExpr) Pos() Pos {
+	return e.LParen
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ParenExpr) End() Pos {
+	return e.RParen + 1
+}
+
+func (e *ParenExpr) String() string {
+	return "(" + e.Expr.String() + ")"
+}
+
+// SelectorExpr represents a selector expression.
+type SelectorExpr struct {
+	Expr Expr
+	Sel  Expr
+}
+
+func (e *SelectorExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *SelectorExpr) Pos() Pos {
+	return e.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *SelectorExpr) End() Pos {
+	return e.Sel.End()
+}
+
+func (e *SelectorExpr) String() string {
+	return e.Expr.String() + "." + e.Sel.String()
+}
+
+// SliceExpr represents a slice expression.
+type SliceExpr struct {
+	Expr   Expr
+	LBrack Pos
+	Low    Expr
+	High   Expr
+	RBrack Pos
+}
+
+func (e *SliceExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *SliceExpr) Pos() Pos {
+	return e.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *SliceExpr) End() Pos {
+	return e.RBrack + 1
+}
+
+func (e *SliceExpr) String() string {
+	var low, high string
+	if e.Low != nil {
+		low = e.Low.String()
+	}
+	if e.High != nil {
+		high = e.High.String()
+	}
+	return e.Expr.String() + "[" + low + ":" + high + "]"
+}
+
+// StringLit represents a string literal.
+type StringLit struct {
+	Value    string
+	ValuePos Pos
+	Literal  string
+}
+
+func (e *StringLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *StringLit) Pos() Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *StringLit) End() Pos {
+	return Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *StringLit) String() string {
+	return e.Literal
+}
+
+// UnaryExpr represents an unary operator expression.
+type UnaryExpr struct {
+	Expr     Expr
+	Token    token.Token
+	TokenPos Pos
+}
+
+func (e *UnaryExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *UnaryExpr) Pos() Pos {
+	return e.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *UnaryExpr) End() Pos {
+	return e.Expr.End()
+}
+
+func (e *UnaryExpr) String() string {
+	return "(" + e.Token.String() + e.Expr.String() + ")"
+}
+
+// UndefinedLit represents an undefined literal.
+type UndefinedLit struct {
+	TokenPos Pos
+}
+
+func (e *UndefinedLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *UndefinedLit) Pos() Pos {
+	return e.TokenPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *UndefinedLit) End() Pos {
+	return e.TokenPos + 9 // len(undefined) == 9
+}
+
+func (e *UndefinedLit) String() string {
+	return "undefined"
+}
diff --git a/vendor/github.com/d5/tengo/v2/parser/file.go b/vendor/github.com/d5/tengo/v2/parser/file.go
new file mode 100644
index 00000000..7cf50fea
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/parser/file.go
@@ -0,0 +1,29 @@
+package parser
+
+import (
+	"strings"
+)
+
+// File represents a file unit.
+type File struct {
+	InputFile *SourceFile
+	Stmts     []Stmt
+}
+
+// Pos returns the position of first character belonging to the node.
+func (n *File) Pos() Pos {
+	return Pos(n.InputFile.Base)
+}
+
+// End returns the position of first character immediately after the node.
+func (n *File) End() Pos {
+	return Pos(n.InputFile.Base + n.InputFile.Size)
+}
+
+func (n *File) String() string {
+	var stmts []string
+	for _, e := range n.Stmts {
+		stmts = append(stmts, e.String())
+	}
+	return strings.Join(stmts, "; ")
+}
diff --git a/vendor/github.com/d5/tengo/v2/parser/opcodes.go b/vendor/github.com/d5/tengo/v2/parser/opcodes.go
new file mode 100644
index 00000000..a4fbfbaf
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/parser/opcodes.go
@@ -0,0 +1,156 @@
+package parser
+
+// Opcode represents a single byte operation code.
+type Opcode = byte
+
+// List of opcodes
+const (
+	OpConstant      Opcode = iota // Load constant
+	OpBComplement                 // bitwise complement
+	OpPop                         // Pop
+	OpTrue                        // Push true
+	OpFalse                       // Push false
+	OpEqual                       // Equal ==
+	OpNotEqual                    // Not equal !=
+	OpMinus                       // Minus -
+	OpLNot                        // Logical not !
+	OpJumpFalsy                   // Jump if falsy
+	OpAndJump                     // Logical AND jump
+	OpOrJump                      // Logical OR jump
+	OpJump                        // Jump
+	OpNull                        // Push null
+	OpArray                       // Array object
+	OpMap                         // Map object
+	OpError                       // Error object
+	OpImmutable                   // Immutable object
+	OpIndex                       // Index operation
+	OpSliceIndex                  // Slice operation
+	OpCall                        // Call function
+	OpReturn                      // Return
+	OpGetGlobal                   // Get global variable
+	OpSetGlobal                   // Set global variable
+	OpSetSelGlobal                // Set global variable using selectors
+	OpGetLocal                    // Get local variable
+	OpSetLocal                    // Set local variable
+	OpDefineLocal                 // Define local variable
+	OpSetSelLocal                 // Set local variable using selectors
+	OpGetFreePtr                  // Get free variable pointer object
+	OpGetFree                     // Get free variables
+	OpSetFree                     // Set free variables
+	OpGetLocalPtr                 // Get local variable as a pointer
+	OpSetSelFree                  // Set free variables using selectors
+	OpGetBuiltin                  // Get builtin function
+	OpClosure                     // Push closure
+	OpIteratorInit                // Iterator init
+	OpIteratorNext                // Iterator next
+	OpIteratorKey                 // Iterator key
+	OpIteratorValue               // Iterator value
+	OpBinaryOp                    // Binary operation
+	OpSuspend                     // Suspend VM
+)
+
+// OpcodeNames are string representation of opcodes.
+var OpcodeNames = [...]string{
+	OpConstant:      "CONST",
+	OpPop:           "POP",
+	OpTrue:          "TRUE",
+	OpFalse:         "FALSE",
+	OpBComplement:   "NEG",
+	OpEqual:         "EQL",
+	OpNotEqual:      "NEQ",
+	OpMinus:         "NEG",
+	OpLNot:          "NOT",
+	OpJumpFalsy:     "JMPF",
+	OpAndJump:       "ANDJMP",
+	OpOrJump:        "ORJMP",
+	OpJump:          "JMP",
+	OpNull:          "NULL",
+	OpGetGlobal:     "GETG",
+	OpSetGlobal:     "SETG",
+	OpSetSelGlobal:  "SETSG",
+	OpArray:         "ARR",
+	OpMap:           "MAP",
+	OpError:         "ERROR",
+	OpImmutable:     "IMMUT",
+	OpIndex:         "INDEX",
+	OpSliceIndex:    "SLICE",
+	OpCall:          "CALL",
+	OpReturn:        "RET",
+	OpGetLocal:      "GETL",
+	OpSetLocal:      "SETL",
+	OpDefineLocal:   "DEFL",
+	OpSetSelLocal:   "SETSL",
+	OpGetBuiltin:    "BUILTIN",
+	OpClosure:       "CLOSURE",
+	OpGetFreePtr:    "GETFP",
+	OpGetFree:       "GETF",
+	OpSetFree:       "SETF",
+	OpGetLocalPtr:   "GETLP",
+	OpSetSelFree:    "SETSF",
+	OpIteratorInit:  "ITER",
+	OpIteratorNext:  "ITNXT",
+	OpIteratorKey:   "ITKEY",
+	OpIteratorValue: "ITVAL",
+	OpBinaryOp:      "BINARYOP",
+	OpSuspend:       "SUSPEND",
+}
+
+// OpcodeOperands is the number of operands.
+var OpcodeOperands = [...][]int{
+	OpConstant:      {2},
+	OpPop:           {},
+	OpTrue:          {},
+	OpFalse:         {},
+	OpBComplement:   {},
+	OpEqual:         {},
+	OpNotEqual:      {},
+	OpMinus:         {},
+	OpLNot:          {},
+	OpJumpFalsy:     {2},
+	OpAndJump:       {2},
+	OpOrJump:        {2},
+	OpJump:          {2},
+	OpNull:          {},
+	OpGetGlobal:     {2},
+	OpSetGlobal:     {2},
+	OpSetSelGlobal:  {2, 1},
+	OpArray:         {2},
+	OpMap:           {2},
+	OpError:         {},
+	OpImmutable:     {},
+	OpIndex:         {},
+	OpSliceIndex:    {},
+	OpCall:          {1},
+	OpReturn:        {1},
+	OpGetLocal:      {1},
+	OpSetLocal:      {1},
+	OpDefineLocal:   {1},
+	OpSetSelLocal:   {1, 1},
+	OpGetBuiltin:    {1},
+	OpClosure:       {2, 1},
+	OpGetFreePtr:    {1},
+	OpGetFree:       {1},
+	OpSetFree:       {1},
+	OpGetLocalPtr:   {1},
+	OpSetSelFree:    {1, 1},
+	OpIteratorInit:  {},
+	OpIteratorNext:  {},
+	OpIteratorKey:   {},
+	OpIteratorValue: {},
+	OpBinaryOp:      {1},
+	OpSuspend:       {},
+}
+
+// ReadOperands reads operands from the bytecode.
+func ReadOperands(numOperands []int, ins []byte) (operands []int, offset int) {
+	for _, width := range numOperands {
+		switch width {
+		case 1:
+			operands = append(operands, int(ins[offset]))
+		case 2:
+			operands = append(operands, int(ins[offset+1])|int(ins[offset])<<8)
+		}
+		offset += width
+	}
+	return
+}
diff --git a/vendor/github.com/d5/tengo/v2/parser/parser.go b/vendor/github.com/d5/tengo/v2/parser/parser.go
new file mode 100644
index 00000000..501a9106
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/parser/parser.go
@@ -0,0 +1,1196 @@
+package parser
+
+import (
+	"fmt"
+	"io"
+	"sort"
+	"strconv"
+
+	"github.com/d5/tengo/v2/token"
+)
+
+type bailout struct{}
+
+var stmtStart = map[token.Token]bool{
+	token.Break:    true,
+	token.Continue: true,
+	token.For:      true,
+	token.If:       true,
+	token.Return:   true,
+	token.Export:   true,
+}
+
+// Error represents a parser error.
+type Error struct {
+	Pos SourceFilePos
+	Msg string
+}
+
+func (e Error) Error() string {
+	if e.Pos.Filename != "" || e.Pos.IsValid() {
+		return fmt.Sprintf("Parse Error: %s\n\tat %s", e.Msg, e.Pos)
+	}
+	return fmt.Sprintf("Parse Error: %s", e.Msg)
+}
+
+// ErrorList is a collection of parser errors.
+type ErrorList []*Error
+
+// Add adds a new parser error to the collection.
+func (p *ErrorList) Add(pos SourceFilePos, msg string) {
+	*p = append(*p, &Error{pos, msg})
+}
+
+// Len returns the number of elements in the collection.
+func (p ErrorList) Len() int {
+	return len(p)
+}
+
+func (p ErrorList) Swap(i, j int) {
+	p[i], p[j] = p[j], p[i]
+}
+
+func (p ErrorList) Less(i, j int) bool {
+	e := &p[i].Pos
+	f := &p[j].Pos
+
+	if e.Filename != f.Filename {
+		return e.Filename < f.Filename
+	}
+	if e.Line != f.Line {
+		return e.Line < f.Line
+	}
+	if e.Column != f.Column {
+		return e.Column < f.Column
+	}
+	return p[i].Msg < p[j].Msg
+}
+
+// Sort sorts the collection.
+func (p ErrorList) Sort() {
+	sort.Sort(p)
+}
+
+func (p ErrorList) Error() string {
+	switch len(p) {
+	case 0:
+		return "no errors"
+	case 1:
+		return p[0].Error()
+	}
+	return fmt.Sprintf("%s (and %d more errors)", p[0], len(p)-1)
+}
+
+// Err returns an error.
+func (p ErrorList) Err() error {
+	if len(p) == 0 {
+		return nil
+	}
+	return p
+}
+
+// Parser parses the Tengo source files. It's based on Go's parser
+// implementation.
+type Parser struct {
+	file      *SourceFile
+	errors    ErrorList
+	scanner   *Scanner
+	pos       Pos
+	token     token.Token
+	tokenLit  string
+	exprLevel int // < 0: in control clause, >= 0: in expression
+	syncPos   Pos // last sync position
+	syncCount int // number of advance calls without progress
+	trace     bool
+	indent    int
+	traceOut  io.Writer
+}
+
+// NewParser creates a Parser.
+func NewParser(file *SourceFile, src []byte, trace io.Writer) *Parser {
+	p := &Parser{
+		file:     file,
+		trace:    trace != nil,
+		traceOut: trace,
+	}
+	p.scanner = NewScanner(p.file, src,
+		func(pos SourceFilePos, msg string) {
+			p.errors.Add(pos, msg)
+		}, 0)
+	p.next()
+	return p
+}
+
+// ParseFile parses the source and returns an AST file unit.
+func (p *Parser) ParseFile() (file *File, err error) {
+	defer func() {
+		if e := recover(); e != nil {
+			if _, ok := e.(bailout); !ok {
+				panic(e)
+			}
+		}
+
+		p.errors.Sort()
+		err = p.errors.Err()
+	}()
+
+	if p.trace {
+		defer untracep(tracep(p, "File"))
+	}
+
+	if p.errors.Len() > 0 {
+		return nil, p.errors.Err()
+	}
+
+	stmts := p.parseStmtList()
+	if p.errors.Len() > 0 {
+		return nil, p.errors.Err()
+	}
+
+	file = &File{
+		InputFile: p.file,
+		Stmts:     stmts,
+	}
+	return
+}
+
+func (p *Parser) parseExpr() Expr {
+	if p.trace {
+		defer untracep(tracep(p, "Expression"))
+	}
+
+	expr := p.parseBinaryExpr(token.LowestPrec + 1)
+
+	// ternary conditional expression
+	if p.token == token.Question {
+		return p.parseCondExpr(expr)
+	}
+	return expr
+}
+
+func (p *Parser) parseBinaryExpr(prec1 int) Expr {
+	if p.trace {
+		defer untracep(tracep(p, "BinaryExpression"))
+	}
+
+	x := p.parseUnaryExpr()
+
+	for {
+		op, prec := p.token, p.token.Precedence()
+		if prec < prec1 {
+			return x
+		}
+
+		pos := p.expect(op)
+
+		y := p.parseBinaryExpr(prec + 1)
+
+		x = &BinaryExpr{
+			LHS:      x,
+			RHS:      y,
+			Token:    op,
+			TokenPos: pos,
+		}
+	}
+}
+
+func (p *Parser) parseCondExpr(cond Expr) Expr {
+	questionPos := p.expect(token.Question)
+	trueExpr := p.parseExpr()
+	colonPos := p.expect(token.Colon)
+	falseExpr := p.parseExpr()
+
+	return &CondExpr{
+		Cond:        cond,
+		True:        trueExpr,
+		False:       falseExpr,
+		QuestionPos: questionPos,
+		ColonPos:    colonPos,
+	}
+}
+
+func (p *Parser) parseUnaryExpr() Expr {
+	if p.trace {
+		defer untracep(tracep(p, "UnaryExpression"))
+	}
+
+	switch p.token {
+	case token.Add, token.Sub, token.Not, token.Xor:
+		pos, op := p.pos, p.token
+		p.next()
+		x := p.parseUnaryExpr()
+		return &UnaryExpr{
+			Token:    op,
+			TokenPos: pos,
+			Expr:     x,
+		}
+	}
+	return p.parsePrimaryExpr()
+}
+
+func (p *Parser) parsePrimaryExpr() Expr {
+	if p.trace {
+		defer untracep(tracep(p, "PrimaryExpression"))
+	}
+
+	x := p.parseOperand()
+
+L:
+	for {
+		switch p.token {
+		case token.Period:
+			p.next()
+
+			switch p.token {
+			case token.Ident:
+				x = p.parseSelector(x)
+			default:
+				pos := p.pos
+				p.errorExpected(pos, "selector")
+				p.advance(stmtStart)
+				return &BadExpr{From: pos, To: p.pos}
+			}
+		case token.LBrack:
+			x = p.parseIndexOrSlice(x)
+		case token.LParen:
+			x = p.parseCall(x)
+		default:
+			break L
+		}
+	}
+	return x
+}
+
+func (p *Parser) parseCall(x Expr) *CallExpr {
+	if p.trace {
+		defer untracep(tracep(p, "Call"))
+	}
+
+	lparen := p.expect(token.LParen)
+	p.exprLevel++
+
+	var list []Expr
+	for p.token != token.RParen && p.token != token.EOF {
+		list = append(list, p.parseExpr())
+
+		if !p.expectComma(token.RParen, "call argument") {
+			break
+		}
+	}
+
+	p.exprLevel--
+	rparen := p.expect(token.RParen)
+	return &CallExpr{
+		Func:   x,
+		LParen: lparen,
+		RParen: rparen,
+		Args:   list,
+	}
+}
+
+func (p *Parser) expectComma(closing token.Token, want string) bool {
+	if p.token == token.Comma {
+		p.next()
+
+		if p.token == closing {
+			p.errorExpected(p.pos, want)
+			return false
+		}
+		return true
+	}
+
+	if p.token == token.Semicolon && p.tokenLit == "\n" {
+		p.next()
+	}
+	return false
+}
+
+func (p *Parser) parseIndexOrSlice(x Expr) Expr {
+	if p.trace {
+		defer untracep(tracep(p, "IndexOrSlice"))
+	}
+
+	lbrack := p.expect(token.LBrack)
+	p.exprLevel++
+
+	var index [2]Expr
+	if p.token != token.Colon {
+		index[0] = p.parseExpr()
+	}
+	numColons := 0
+	if p.token == token.Colon {
+		numColons++
+		p.next()
+
+		if p.token != token.RBrack && p.token != token.EOF {
+			index[1] = p.parseExpr()
+		}
+	}
+
+	p.exprLevel--
+	rbrack := p.expect(token.RBrack)
+
+	if numColons > 0 {
+		// slice expression
+		return &SliceExpr{
+			Expr:   x,
+			LBrack: lbrack,
+			RBrack: rbrack,
+			Low:    index[0],
+			High:   index[1],
+		}
+	}
+	return &IndexExpr{
+		Expr:   x,
+		LBrack: lbrack,
+		RBrack: rbrack,
+		Index:  index[0],
+	}
+}
+
+func (p *Parser) parseSelector(x Expr) Expr {
+	if p.trace {
+		defer untracep(tracep(p, "Selector"))
+	}
+
+	sel := p.parseIdent()
+	return &SelectorExpr{Expr: x, Sel: &StringLit{
+		Value:    sel.Name,
+		ValuePos: sel.NamePos,
+		Literal:  sel.Name,
+	}}
+}
+
+func (p *Parser) parseOperand() Expr {
+	if p.trace {
+		defer untracep(tracep(p, "Operand"))
+	}
+
+	switch p.token {
+	case token.Ident:
+		return p.parseIdent()
+	case token.Int:
+		v, _ := strconv.ParseInt(p.tokenLit, 10, 64)
+		x := &IntLit{
+			Value:    v,
+			ValuePos: p.pos,
+			Literal:  p.tokenLit,
+		}
+		p.next()
+		return x
+	case token.Float:
+		v, _ := strconv.ParseFloat(p.tokenLit, 64)
+		x := &FloatLit{
+			Value:    v,
+			ValuePos: p.pos,
+			Literal:  p.tokenLit,
+		}
+		p.next()
+		return x
+	case token.Char:
+		return p.parseCharLit()
+	case token.String:
+		v, _ := strconv.Unquote(p.tokenLit)
+		x := &StringLit{
+			Value:    v,
+			ValuePos: p.pos,
+			Literal:  p.tokenLit,
+		}
+		p.next()
+		return x
+	case token.True:
+		x := &BoolLit{
+			Value:    true,
+			ValuePos: p.pos,
+			Literal:  p.tokenLit,
+		}
+		p.next()
+		return x
+	case token.False:
+		x := &BoolLit{
+			Value:    false,
+			ValuePos: p.pos,
+			Literal:  p.tokenLit,
+		}
+		p.next()
+		return x
+	case token.Undefined:
+		x := &UndefinedLit{TokenPos: p.pos}
+		p.next()
+		return x
+	case token.Import:
+		return p.parseImportExpr()
+	case token.LParen:
+		lparen := p.pos
+		p.next()
+		p.exprLevel++
+		x := p.parseExpr()
+		p.exprLevel--
+		rparen := p.expect(token.RParen)
+		return &ParenExpr{
+			LParen: lparen,
+			Expr:   x,
+			RParen: rparen,
+		}
+	case token.LBrack: // array literal
+		return p.parseArrayLit()
+	case token.LBrace: // map literal
+		return p.parseMapLit()
+	case token.Func: // function literal
+		return p.parseFuncLit()
+	case token.Error: // error expression
+		return p.parseErrorExpr()
+	case token.Immutable: // immutable expression
+		return p.parseImmutableExpr()
+	}
+
+	pos := p.pos
+	p.errorExpected(pos, "operand")
+	p.advance(stmtStart)
+	return &BadExpr{From: pos, To: p.pos}
+}
+
+func (p *Parser) parseImportExpr() Expr {
+	pos := p.pos
+	p.next()
+	p.expect(token.LParen)
+	if p.token != token.String {
+		p.errorExpected(p.pos, "module name")
+		p.advance(stmtStart)
+		return &BadExpr{From: pos, To: p.pos}
+	}
+
+	// module name
+	moduleName, _ := strconv.Unquote(p.tokenLit)
+	expr := &ImportExpr{
+		ModuleName: moduleName,
+		Token:      token.Import,
+		TokenPos:   pos,
+	}
+
+	p.next()
+	p.expect(token.RParen)
+	return expr
+}
+
+func (p *Parser) parseCharLit() Expr {
+	if n := len(p.tokenLit); n >= 3 {
+		code, _, _, err := strconv.UnquoteChar(p.tokenLit[1:n-1], '\'')
+		if err == nil {
+			x := &CharLit{
+				Value:    code,
+				ValuePos: p.pos,
+				Literal:  p.tokenLit,
+			}
+			p.next()
+			return x
+		}
+	}
+
+	pos := p.pos
+	p.error(pos, "illegal char literal")
+	p.next()
+	return &BadExpr{
+		From: pos,
+		To:   p.pos,
+	}
+}
+
+func (p *Parser) parseFuncLit() Expr {
+	if p.trace {
+		defer untracep(tracep(p, "FuncLit"))
+	}
+
+	typ := p.parseFuncType()
+	p.exprLevel++
+	body := p.parseBody()
+	p.exprLevel--
+	return &FuncLit{
+		Type: typ,
+		Body: body,
+	}
+}
+
+func (p *Parser) parseArrayLit() Expr {
+	if p.trace {
+		defer untracep(tracep(p, "ArrayLit"))
+	}
+
+	lbrack := p.expect(token.LBrack)
+	p.exprLevel++
+
+	var elements []Expr
+	for p.token != token.RBrack && p.token != token.EOF {
+		elements = append(elements, p.parseExpr())
+
+		if !p.expectComma(token.RBrack, "array element") {
+			break
+		}
+	}
+
+	p.exprLevel--
+	rbrack := p.expect(token.RBrack)
+	return &ArrayLit{
+		Elements: elements,
+		LBrack:   lbrack,
+		RBrack:   rbrack,
+	}
+}
+
+func (p *Parser) parseErrorExpr() Expr {
+	pos := p.pos
+
+	p.next()
+	lparen := p.expect(token.LParen)
+	value := p.parseExpr()
+	rparen := p.expect(token.RParen)
+	return &ErrorExpr{
+		ErrorPos: pos,
+		Expr:     value,
+		LParen:   lparen,
+		RParen:   rparen,
+	}
+}
+
+func (p *Parser) parseImmutableExpr() Expr {
+	pos := p.pos
+
+	p.next()
+	lparen := p.expect(token.LParen)
+	value := p.parseExpr()
+	rparen := p.expect(token.RParen)
+	return &ImmutableExpr{
+		ErrorPos: pos,
+		Expr:     value,
+		LParen:   lparen,
+		RParen:   rparen,
+	}
+}
+
+func (p *Parser) parseFuncType() *FuncType {
+	if p.trace {
+		defer untracep(tracep(p, "FuncType"))
+	}
+
+	pos := p.expect(token.Func)
+	params := p.parseIdentList()
+	return &FuncType{
+		FuncPos: pos,
+		Params:  params,
+	}
+}
+
+func (p *Parser) parseBody() *BlockStmt {
+	if p.trace {
+		defer untracep(tracep(p, "Body"))
+	}
+
+	lbrace := p.expect(token.LBrace)
+	list := p.parseStmtList()
+	rbrace := p.expect(token.RBrace)
+	return &BlockStmt{
+		LBrace: lbrace,
+		RBrace: rbrace,
+		Stmts:  list,
+	}
+}
+
+func (p *Parser) parseStmtList() (list []Stmt) {
+	if p.trace {
+		defer untracep(tracep(p, "StatementList"))
+	}
+
+	for p.token != token.RBrace && p.token != token.EOF {
+		list = append(list, p.parseStmt())
+	}
+	return
+}
+
+func (p *Parser) parseIdent() *Ident {
+	pos := p.pos
+	name := "_"
+
+	if p.token == token.Ident {
+		name = p.tokenLit
+		p.next()
+	} else {
+		p.expect(token.Ident)
+	}
+	return &Ident{
+		NamePos: pos,
+		Name:    name,
+	}
+}
+
+func (p *Parser) parseIdentList() *IdentList {
+	if p.trace {
+		defer untracep(tracep(p, "IdentList"))
+	}
+
+	var params []*Ident
+	lparen := p.expect(token.LParen)
+	isVarArgs := false
+	if p.token != token.RParen {
+		if p.token == token.Ellipsis {
+			isVarArgs = true
+			p.next()
+		}
+
+		params = append(params, p.parseIdent())
+		for !isVarArgs && p.token == token.Comma {
+			p.next()
+			if p.token == token.Ellipsis {
+				isVarArgs = true
+				p.next()
+			}
+			params = append(params, p.parseIdent())
+		}
+	}
+
+	rparen := p.expect(token.RParen)
+	return &IdentList{
+		LParen:  lparen,
+		RParen:  rparen,
+		VarArgs: isVarArgs,
+		List:    params,
+	}
+}
+
+func (p *Parser) parseStmt() (stmt Stmt) {
+	if p.trace {
+		defer untracep(tracep(p, "Statement"))
+	}
+
+	switch p.token {
+	case // simple statements
+		token.Func, token.Error, token.Immutable, token.Ident, token.Int,
+		token.Float, token.Char, token.String, token.True, token.False,
+		token.Undefined, token.Import, token.LParen, token.LBrace,
+		token.LBrack, token.Add, token.Sub, token.Mul, token.And, token.Xor,
+		token.Not:
+		s := p.parseSimpleStmt(false)
+		p.expectSemi()
+		return s
+	case token.Return:
+		return p.parseReturnStmt()
+	case token.Export:
+		return p.parseExportStmt()
+	case token.If:
+		return p.parseIfStmt()
+	case token.For:
+		return p.parseForStmt()
+	case token.Break, token.Continue:
+		return p.parseBranchStmt(p.token)
+	case token.Semicolon:
+		s := &EmptyStmt{Semicolon: p.pos, Implicit: p.tokenLit == "\n"}
+		p.next()
+		return s
+	case token.RBrace:
+		// semicolon may be omitted before a closing "}"
+		return &EmptyStmt{Semicolon: p.pos, Implicit: true}
+	default:
+		pos := p.pos
+		p.errorExpected(pos, "statement")
+		p.advance(stmtStart)
+		return &BadStmt{From: pos, To: p.pos}
+	}
+}
+
+func (p *Parser) parseForStmt() Stmt {
+	if p.trace {
+		defer untracep(tracep(p, "ForStmt"))
+	}
+
+	pos := p.expect(token.For)
+
+	// for {}
+	if p.token == token.LBrace {
+		body := p.parseBlockStmt()
+		p.expectSemi()
+
+		return &ForStmt{
+			ForPos: pos,
+			Body:   body,
+		}
+	}
+
+	prevLevel := p.exprLevel
+	p.exprLevel = -1
+
+	var s1 Stmt
+	if p.token != token.Semicolon { // skipping init
+		s1 = p.parseSimpleStmt(true)
+	}
+
+	// for _ in seq {}            or
+	// for value in seq {}        or
+	// for key, value in seq {}
+	if forInStmt, isForIn := s1.(*ForInStmt); isForIn {
+		forInStmt.ForPos = pos
+		p.exprLevel = prevLevel
+		forInStmt.Body = p.parseBlockStmt()
+		p.expectSemi()
+		return forInStmt
+	}
+
+	// for init; cond; post {}
+	var s2, s3 Stmt
+	if p.token == token.Semicolon {
+		p.next()
+		if p.token != token.Semicolon {
+			s2 = p.parseSimpleStmt(false) // cond
+		}
+		p.expect(token.Semicolon)
+		if p.token != token.LBrace {
+			s3 = p.parseSimpleStmt(false) // post
+		}
+	} else {
+		// for cond {}
+		s2 = s1
+		s1 = nil
+	}
+
+	// body
+	p.exprLevel = prevLevel
+	body := p.parseBlockStmt()
+	p.expectSemi()
+	cond := p.makeExpr(s2, "condition expression")
+	return &ForStmt{
+		ForPos: pos,
+		Init:   s1,
+		Cond:   cond,
+		Post:   s3,
+		Body:   body,
+	}
+}
+
+func (p *Parser) parseBranchStmt(tok token.Token) Stmt {
+	if p.trace {
+		defer untracep(tracep(p, "BranchStmt"))
+	}
+
+	pos := p.expect(tok)
+
+	var label *Ident
+	if p.token == token.Ident {
+		label = p.parseIdent()
+	}
+	p.expectSemi()
+	return &BranchStmt{
+		Token:    tok,
+		TokenPos: pos,
+		Label:    label,
+	}
+}
+
+func (p *Parser) parseIfStmt() Stmt {
+	if p.trace {
+		defer untracep(tracep(p, "IfStmt"))
+	}
+
+	pos := p.expect(token.If)
+	init, cond := p.parseIfHeader()
+	body := p.parseBlockStmt()
+
+	var elseStmt Stmt
+	if p.token == token.Else {
+		p.next()
+
+		switch p.token {
+		case token.If:
+			elseStmt = p.parseIfStmt()
+		case token.LBrace:
+			elseStmt = p.parseBlockStmt()
+			p.expectSemi()
+		default:
+			p.errorExpected(p.pos, "if or {")
+			elseStmt = &BadStmt{From: p.pos, To: p.pos}
+		}
+	} else {
+		p.expectSemi()
+	}
+	return &IfStmt{
+		IfPos: pos,
+		Init:  init,
+		Cond:  cond,
+		Body:  body,
+		Else:  elseStmt,
+	}
+}
+
+func (p *Parser) parseBlockStmt() *BlockStmt {
+	if p.trace {
+		defer untracep(tracep(p, "BlockStmt"))
+	}
+
+	lbrace := p.expect(token.LBrace)
+	list := p.parseStmtList()
+	rbrace := p.expect(token.RBrace)
+	return &BlockStmt{
+		LBrace: lbrace,
+		RBrace: rbrace,
+		Stmts:  list,
+	}
+}
+
+func (p *Parser) parseIfHeader() (init Stmt, cond Expr) {
+	if p.token == token.LBrace {
+		p.error(p.pos, "missing condition in if statement")
+		cond = &BadExpr{From: p.pos, To: p.pos}
+		return
+	}
+
+	outer := p.exprLevel
+	p.exprLevel = -1
+	if p.token == token.Semicolon {
+		p.error(p.pos, "missing init in if statement")
+		return
+	}
+	init = p.parseSimpleStmt(false)
+
+	var condStmt Stmt
+	if p.token == token.LBrace {
+		condStmt = init
+		init = nil
+	} else if p.token == token.Semicolon {
+		p.next()
+
+		condStmt = p.parseSimpleStmt(false)
+	} else {
+		p.error(p.pos, "missing condition in if statement")
+	}
+
+	if condStmt != nil {
+		cond = p.makeExpr(condStmt, "boolean expression")
+	}
+	if cond == nil {
+		cond = &BadExpr{From: p.pos, To: p.pos}
+	}
+	p.exprLevel = outer
+	return
+}
+
+func (p *Parser) makeExpr(s Stmt, want string) Expr {
+	if s == nil {
+		return nil
+	}
+
+	if es, isExpr := s.(*ExprStmt); isExpr {
+		return es.Expr
+	}
+
+	found := "simple statement"
+	if _, isAss := s.(*AssignStmt); isAss {
+		found = "assignment"
+	}
+	p.error(s.Pos(), fmt.Sprintf("expected %s, found %s", want, found))
+	return &BadExpr{From: s.Pos(), To: p.safePos(s.End())}
+}
+
+func (p *Parser) parseReturnStmt() Stmt {
+	if p.trace {
+		defer untracep(tracep(p, "ReturnStmt"))
+	}
+
+	pos := p.pos
+	p.expect(token.Return)
+
+	var x Expr
+	if p.token != token.Semicolon && p.token != token.RBrace {
+		x = p.parseExpr()
+	}
+	p.expectSemi()
+	return &ReturnStmt{
+		ReturnPos: pos,
+		Result:    x,
+	}
+}
+
+func (p *Parser) parseExportStmt() Stmt {
+	if p.trace {
+		defer untracep(tracep(p, "ExportStmt"))
+	}
+
+	pos := p.pos
+	p.expect(token.Export)
+	x := p.parseExpr()
+	p.expectSemi()
+	return &ExportStmt{
+		ExportPos: pos,
+		Result:    x,
+	}
+}
+
+func (p *Parser) parseSimpleStmt(forIn bool) Stmt {
+	if p.trace {
+		defer untracep(tracep(p, "SimpleStmt"))
+	}
+
+	x := p.parseExprList()
+
+	switch p.token {
+	case token.Assign, token.Define: // assignment statement
+		pos, tok := p.pos, p.token
+		p.next()
+		y := p.parseExprList()
+		return &AssignStmt{
+			LHS:      x,
+			RHS:      y,
+			Token:    tok,
+			TokenPos: pos,
+		}
+	case token.In:
+		if forIn {
+			p.next()
+			y := p.parseExpr()
+
+			var key, value *Ident
+			var ok bool
+			switch len(x) {
+			case 1:
+				key = &Ident{Name: "_", NamePos: x[0].Pos()}
+
+				value, ok = x[0].(*Ident)
+				if !ok {
+					p.errorExpected(x[0].Pos(), "identifier")
+					value = &Ident{Name: "_", NamePos: x[0].Pos()}
+				}
+			case 2:
+				key, ok = x[0].(*Ident)
+				if !ok {
+					p.errorExpected(x[0].Pos(), "identifier")
+					key = &Ident{Name: "_", NamePos: x[0].Pos()}
+				}
+				value, ok = x[1].(*Ident)
+				if !ok {
+					p.errorExpected(x[1].Pos(), "identifier")
+					value = &Ident{Name: "_", NamePos: x[1].Pos()}
+				}
+			}
+			return &ForInStmt{
+				Key:      key,
+				Value:    value,
+				Iterable: y,
+			}
+		}
+	}
+
+	if len(x) > 1 {
+		p.errorExpected(x[0].Pos(), "1 expression")
+		// continue with first expression
+	}
+
+	switch p.token {
+	case token.Define,
+		token.AddAssign, token.SubAssign, token.MulAssign, token.QuoAssign,
+		token.RemAssign, token.AndAssign, token.OrAssign, token.XorAssign,
+		token.ShlAssign, token.ShrAssign, token.AndNotAssign:
+		pos, tok := p.pos, p.token
+		p.next()
+		y := p.parseExpr()
+		return &AssignStmt{
+			LHS:      []Expr{x[0]},
+			RHS:      []Expr{y},
+			Token:    tok,
+			TokenPos: pos,
+		}
+	case token.Inc, token.Dec:
+		// increment or decrement statement
+		s := &IncDecStmt{Expr: x[0], Token: p.token, TokenPos: p.pos}
+		p.next()
+		return s
+	}
+	return &ExprStmt{Expr: x[0]}
+}
+
+func (p *Parser) parseExprList() (list []Expr) {
+	if p.trace {
+		defer untracep(tracep(p, "ExpressionList"))
+	}
+
+	list = append(list, p.parseExpr())
+	for p.token == token.Comma {
+		p.next()
+		list = append(list, p.parseExpr())
+	}
+	return
+}
+
+func (p *Parser) parseMapElementLit() *MapElementLit {
+	if p.trace {
+		defer untracep(tracep(p, "MapElementLit"))
+	}
+
+	pos := p.pos
+	name := "_"
+	if p.token == token.Ident {
+		name = p.tokenLit
+	} else if p.token == token.String {
+		v, _ := strconv.Unquote(p.tokenLit)
+		name = v
+	} else {
+		p.errorExpected(pos, "map key")
+	}
+	p.next()
+	colonPos := p.expect(token.Colon)
+	valueExpr := p.parseExpr()
+	return &MapElementLit{
+		Key:      name,
+		KeyPos:   pos,
+		ColonPos: colonPos,
+		Value:    valueExpr,
+	}
+}
+
+func (p *Parser) parseMapLit() *MapLit {
+	if p.trace {
+		defer untracep(tracep(p, "MapLit"))
+	}
+
+	lbrace := p.expect(token.LBrace)
+	p.exprLevel++
+
+	var elements []*MapElementLit
+	for p.token != token.RBrace && p.token != token.EOF {
+		elements = append(elements, p.parseMapElementLit())
+
+		if !p.expectComma(token.RBrace, "map element") {
+			break
+		}
+	}
+
+	p.exprLevel--
+	rbrace := p.expect(token.RBrace)
+	return &MapLit{
+		LBrace:   lbrace,
+		RBrace:   rbrace,
+		Elements: elements,
+	}
+}
+
+func (p *Parser) expect(token token.Token) Pos {
+	pos := p.pos
+
+	if p.token != token {
+		p.errorExpected(pos, "'"+token.String()+"'")
+	}
+	p.next()
+	return pos
+}
+
+func (p *Parser) expectSemi() {
+	switch p.token {
+	case token.RParen, token.RBrace:
+		// semicolon is optional before a closing ')' or '}'
+	case token.Comma:
+		// permit a ',' instead of a ';' but complain
+		p.errorExpected(p.pos, "';'")
+		fallthrough
+	case token.Semicolon:
+		p.next()
+	default:
+		p.errorExpected(p.pos, "';'")
+		p.advance(stmtStart)
+	}
+}
+
+func (p *Parser) advance(to map[token.Token]bool) {
+	for ; p.token != token.EOF; p.next() {
+		if to[p.token] {
+			if p.pos == p.syncPos && p.syncCount < 10 {
+				p.syncCount++
+				return
+			}
+			if p.pos > p.syncPos {
+				p.syncPos = p.pos
+				p.syncCount = 0
+				return
+			}
+		}
+	}
+}
+
+func (p *Parser) error(pos Pos, msg string) {
+	filePos := p.file.Position(pos)
+
+	n := len(p.errors)
+	if n > 0 && p.errors[n-1].Pos.Line == filePos.Line {
+		// discard errors reported on the same line
+		return
+	}
+	if n > 10 {
+		// too many errors; terminate early
+		panic(bailout{})
+	}
+	p.errors.Add(filePos, msg)
+}
+
+func (p *Parser) errorExpected(pos Pos, msg string) {
+	msg = "expected " + msg
+	if pos == p.pos {
+		// error happened at the current position: provide more specific
+		switch {
+		case p.token == token.Semicolon && p.tokenLit == "\n":
+			msg += ", found newline"
+		case p.token.IsLiteral():
+			msg += ", found " + p.tokenLit
+		default:
+			msg += ", found '" + p.token.String() + "'"
+		}
+	}
+	p.error(pos, msg)
+}
+
+func (p *Parser) next() {
+	if p.trace && p.pos.IsValid() {
+		s := p.token.String()
+		switch {
+		case p.token.IsLiteral():
+			p.printTrace(s, p.tokenLit)
+		case p.token.IsOperator(), p.token.IsKeyword():
+			p.printTrace(`"` + s + `"`)
+		default:
+			p.printTrace(s)
+		}
+	}
+	p.token, p.tokenLit, p.pos = p.scanner.Scan()
+}
+
+func (p *Parser) printTrace(a ...interface{}) {
+	const (
+		dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
+		n    = len(dots)
+	)
+
+	filePos := p.file.Position(p.pos)
+	_, _ = fmt.Fprintf(p.traceOut, "%5d: %5d:%3d: ", p.pos, filePos.Line,
+		filePos.Column)
+	i := 2 * p.indent
+	for i > n {
+		_, _ = fmt.Fprint(p.traceOut, dots)
+		i -= n
+	}
+	_, _ = fmt.Fprint(p.traceOut, dots[0:i])
+	_, _ = fmt.Fprintln(p.traceOut, a...)
+}
+
+func (p *Parser) safePos(pos Pos) Pos {
+	fileBase := p.file.Base
+	fileSize := p.file.Size
+
+	if int(pos) < fileBase || int(pos) > fileBase+fileSize {
+		return Pos(fileBase + fileSize)
+	}
+	return pos
+}
+
+func tracep(p *Parser, msg string) *Parser {
+	p.printTrace(msg, "(")
+	p.indent++
+	return p
+}
+
+func untracep(p *Parser) {
+	p.indent--
+	p.printTrace(")")
+}
diff --git a/vendor/github.com/d5/tengo/v2/parser/pos.go b/vendor/github.com/d5/tengo/v2/parser/pos.go
new file mode 100644
index 00000000..f8d3898c
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/parser/pos.go
@@ -0,0 +1,12 @@
+package parser
+
+// Pos represents a position in the file set.
+type Pos int
+
+// NoPos represents an invalid position.
+const NoPos Pos = 0
+
+// IsValid returns true if the position is valid.
+func (p Pos) IsValid() bool {
+	return p != NoPos
+}
diff --git a/vendor/github.com/d5/tengo/v2/parser/scanner.go b/vendor/github.com/d5/tengo/v2/parser/scanner.go
new file mode 100644
index 00000000..f1d820a4
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/parser/scanner.go
@@ -0,0 +1,689 @@
+package parser
+
+import (
+	"fmt"
+	"unicode"
+	"unicode/utf8"
+
+	"github.com/d5/tengo/v2/token"
+)
+
+// byte order mark
+const bom = 0xFEFF
+
+// ScanMode represents a scanner mode.
+type ScanMode int
+
+// List of scanner modes.
+const (
+	ScanComments ScanMode = 1 << iota
+	DontInsertSemis
+)
+
+// ScannerErrorHandler is an error handler for the scanner.
+type ScannerErrorHandler func(pos SourceFilePos, msg string)
+
+// Scanner reads the Tengo source text. It's based on Go's scanner
+// implementation.
+type Scanner struct {
+	file         *SourceFile         // source file handle
+	src          []byte              // source
+	ch           rune                // current character
+	offset       int                 // character offset
+	readOffset   int                 // reading offset (position after current character)
+	lineOffset   int                 // current line offset
+	insertSemi   bool                // insert a semicolon before next newline
+	errorHandler ScannerErrorHandler // error reporting; or nil
+	errorCount   int                 // number of errors encountered
+	mode         ScanMode
+}
+
+// NewScanner creates a Scanner.
+func NewScanner(
+	file *SourceFile,
+	src []byte,
+	errorHandler ScannerErrorHandler,
+	mode ScanMode,
+) *Scanner {
+	if file.Size != len(src) {
+		panic(fmt.Sprintf("file size (%d) does not match src len (%d)",
+			file.Size, len(src)))
+	}
+
+	s := &Scanner{
+		file:         file,
+		src:          src,
+		errorHandler: errorHandler,
+		ch:           ' ',
+		mode:         mode,
+	}
+
+	s.next()
+	if s.ch == bom {
+		s.next() // ignore BOM at file beginning
+	}
+
+	return s
+}
+
+// ErrorCount returns the number of errors.
+func (s *Scanner) ErrorCount() int {
+	return s.errorCount
+}
+
+// Scan returns a token, token literal and its position.
+func (s *Scanner) Scan() (
+	tok token.Token,
+	literal string,
+	pos Pos,
+) {
+	s.skipWhitespace()
+
+	pos = s.file.FileSetPos(s.offset)
+
+	insertSemi := false
+
+	// determine token value
+	switch ch := s.ch; {
+	case isLetter(ch):
+		literal = s.scanIdentifier()
+		tok = token.Lookup(literal)
+		switch tok {
+		case token.Ident, token.Break, token.Continue, token.Return,
+			token.Export, token.True, token.False, token.Undefined:
+			insertSemi = true
+		}
+	case '0' <= ch && ch <= '9':
+		insertSemi = true
+		tok, literal = s.scanNumber(false)
+	default:
+		s.next() // always make progress
+
+		switch ch {
+		case -1: // EOF
+			if s.insertSemi {
+				s.insertSemi = false // EOF consumed
+				return token.Semicolon, "\n", pos
+			}
+			tok = token.EOF
+		case '\n':
+			// we only reach here if s.insertSemi was set in the first place
+			s.insertSemi = false // newline consumed
+			return token.Semicolon, "\n", pos
+		case '"':
+			insertSemi = true
+			tok = token.String
+			literal = s.scanString()
+		case '\'':
+			insertSemi = true
+			tok = token.Char
+			literal = s.scanRune()
+		case '`':
+			insertSemi = true
+			tok = token.String
+			literal = s.scanRawString()
+		case ':':
+			tok = s.switch2(token.Colon, token.Define)
+		case '.':
+			if '0' <= s.ch && s.ch <= '9' {
+				insertSemi = true
+				tok, literal = s.scanNumber(true)
+			} else {
+				tok = token.Period
+				if s.ch == '.' && s.peek() == '.' {
+					s.next()
+					s.next() // consume last '.'
+					tok = token.Ellipsis
+				}
+			}
+		case ',':
+			tok = token.Comma
+		case '?':
+			tok = token.Question
+		case ';':
+			tok = token.Semicolon
+			literal = ";"
+		case '(':
+			tok = token.LParen
+		case ')':
+			insertSemi = true
+			tok = token.RParen
+		case '[':
+			tok = token.LBrack
+		case ']':
+			insertSemi = true
+			tok = token.RBrack
+		case '{':
+			tok = token.LBrace
+		case '}':
+			insertSemi = true
+			tok = token.RBrace
+		case '+':
+			tok = s.switch3(token.Add, token.AddAssign, '+', token.Inc)
+			if tok == token.Inc {
+				insertSemi = true
+			}
+		case '-':
+			tok = s.switch3(token.Sub, token.SubAssign, '-', token.Dec)
+			if tok == token.Dec {
+				insertSemi = true
+			}
+		case '*':
+			tok = s.switch2(token.Mul, token.MulAssign)
+		case '/':
+			if s.ch == '/' || s.ch == '*' {
+				// comment
+				if s.insertSemi && s.findLineEnd() {
+					// reset position to the beginning of the comment
+					s.ch = '/'
+					s.offset = s.file.Offset(pos)
+					s.readOffset = s.offset + 1
+					s.insertSemi = false // newline consumed
+					return token.Semicolon, "\n", pos
+				}
+				comment := s.scanComment()
+				if s.mode&ScanComments == 0 {
+					// skip comment
+					s.insertSemi = false // newline consumed
+					return s.Scan()
+				}
+				tok = token.Comment
+				literal = comment
+			} else {
+				tok = s.switch2(token.Quo, token.QuoAssign)
+			}
+		case '%':
+			tok = s.switch2(token.Rem, token.RemAssign)
+		case '^':
+			tok = s.switch2(token.Xor, token.XorAssign)
+		case '<':
+			tok = s.switch4(token.Less, token.LessEq, '<',
+				token.Shl, token.ShlAssign)
+		case '>':
+			tok = s.switch4(token.Greater, token.GreaterEq, '>',
+				token.Shr, token.ShrAssign)
+		case '=':
+			tok = s.switch2(token.Assign, token.Equal)
+		case '!':
+			tok = s.switch2(token.Not, token.NotEqual)
+		case '&':
+			if s.ch == '^' {
+				s.next()
+				tok = s.switch2(token.AndNot, token.AndNotAssign)
+			} else {
+				tok = s.switch3(token.And, token.AndAssign, '&', token.LAnd)
+			}
+		case '|':
+			tok = s.switch3(token.Or, token.OrAssign, '|', token.LOr)
+		default:
+			// next reports unexpected BOMs - don't repeat
+			if ch != bom {
+				s.error(s.file.Offset(pos),
+					fmt.Sprintf("illegal character %#U", ch))
+			}
+			insertSemi = s.insertSemi // preserve insertSemi info
+			tok = token.Illegal
+			literal = string(ch)
+		}
+	}
+	if s.mode&DontInsertSemis == 0 {
+		s.insertSemi = insertSemi
+	}
+	return
+}
+
+func (s *Scanner) next() {
+	if s.readOffset < len(s.src) {
+		s.offset = s.readOffset
+		if s.ch == '\n' {
+			s.lineOffset = s.offset
+			s.file.AddLine(s.offset)
+		}
+		r, w := rune(s.src[s.readOffset]), 1
+		switch {
+		case r == 0:
+			s.error(s.offset, "illegal character NUL")
+		case r >= utf8.RuneSelf:
+			// not ASCII
+			r, w = utf8.DecodeRune(s.src[s.readOffset:])
+			if r == utf8.RuneError && w == 1 {
+				s.error(s.offset, "illegal UTF-8 encoding")
+			} else if r == bom && s.offset > 0 {
+				s.error(s.offset, "illegal byte order mark")
+			}
+		}
+		s.readOffset += w
+		s.ch = r
+	} else {
+		s.offset = len(s.src)
+		if s.ch == '\n' {
+			s.lineOffset = s.offset
+			s.file.AddLine(s.offset)
+		}
+		s.ch = -1 // eof
+	}
+}
+
+func (s *Scanner) peek() byte {
+	if s.readOffset < len(s.src) {
+		return s.src[s.readOffset]
+	}
+	return 0
+}
+
+func (s *Scanner) error(offset int, msg string) {
+	if s.errorHandler != nil {
+		s.errorHandler(s.file.Position(s.file.FileSetPos(offset)), msg)
+	}
+	s.errorCount++
+}
+
+func (s *Scanner) scanComment() string {
+	// initial '/' already consumed; s.ch == '/' || s.ch == '*'
+	offs := s.offset - 1 // position of initial '/'
+	var numCR int
+
+	if s.ch == '/' {
+		//-style comment
+		// (the final '\n' is not considered part of the comment)
+		s.next()
+		for s.ch != '\n' && s.ch >= 0 {
+			if s.ch == '\r' {
+				numCR++
+			}
+			s.next()
+		}
+		goto exit
+	}
+
+	/*-style comment */
+	s.next()
+	for s.ch >= 0 {
+		ch := s.ch
+		if ch == '\r' {
+			numCR++
+		}
+		s.next()
+		if ch == '*' && s.ch == '/' {
+			s.next()
+			goto exit
+		}
+	}
+
+	s.error(offs, "comment not terminated")
+
+exit:
+	lit := s.src[offs:s.offset]
+
+	// On Windows, a (//-comment) line may end in "\r\n".
+	// Remove the final '\r' before analyzing the text for line directives (matching the compiler).
+	// Remove any other '\r' afterwards (matching the pre-existing behavior of the scanner).
+	if numCR > 0 && len(lit) >= 2 && lit[1] == '/' && lit[len(lit)-1] == '\r' {
+		lit = lit[:len(lit)-1]
+		numCR--
+	}
+	if numCR > 0 {
+		lit = StripCR(lit, lit[1] == '*')
+	}
+	return string(lit)
+}
+
+func (s *Scanner) findLineEnd() bool {
+	// initial '/' already consumed
+
+	defer func(offs int) {
+		// reset scanner state to where it was upon calling findLineEnd
+		s.ch = '/'
+		s.offset = offs
+		s.readOffset = offs + 1
+		s.next() // consume initial '/' again
+	}(s.offset - 1)
+
+	// read ahead until a newline, EOF, or non-comment tok is found
+	for s.ch == '/' || s.ch == '*' {
+		if s.ch == '/' {
+			//-style comment always contains a newline
+			return true
+		}
+		/*-style comment: look for newline */
+		s.next()
+		for s.ch >= 0 {
+			ch := s.ch
+			if ch == '\n' {
+				return true
+			}
+			s.next()
+			if ch == '*' && s.ch == '/' {
+				s.next()
+				break
+			}
+		}
+		s.skipWhitespace() // s.insertSemi is set
+		if s.ch < 0 || s.ch == '\n' {
+			return true
+		}
+		if s.ch != '/' {
+			// non-comment tok
+			return false
+		}
+		s.next() // consume '/'
+	}
+	return false
+}
+
+func (s *Scanner) scanIdentifier() string {
+	offs := s.offset
+	for isLetter(s.ch) || isDigit(s.ch) {
+		s.next()
+	}
+	return string(s.src[offs:s.offset])
+}
+
+func (s *Scanner) scanMantissa(base int) {
+	for digitVal(s.ch) < base {
+		s.next()
+	}
+}
+
+func (s *Scanner) scanNumber(
+	seenDecimalPoint bool,
+) (tok token.Token, lit string) {
+	// digitVal(s.ch) < 10
+	offs := s.offset
+	tok = token.Int
+
+	defer func() {
+		lit = string(s.src[offs:s.offset])
+	}()
+
+	if seenDecimalPoint {
+		offs--
+		tok = token.Float
+		s.scanMantissa(10)
+		goto exponent
+	}
+
+	if s.ch == '0' {
+		// int or float
+		offs := s.offset
+		s.next()
+		if s.ch == 'x' || s.ch == 'X' {
+			// hexadecimal int
+			s.next()
+			s.scanMantissa(16)
+			if s.offset-offs <= 2 {
+				// only scanned "0x" or "0X"
+				s.error(offs, "illegal hexadecimal number")
+			}
+		} else {
+			// octal int or float
+			seenDecimalDigit := false
+			s.scanMantissa(8)
+			if s.ch == '8' || s.ch == '9' {
+				// illegal octal int or float
+				seenDecimalDigit = true
+				s.scanMantissa(10)
+			}
+			if s.ch == '.' || s.ch == 'e' || s.ch == 'E' || s.ch == 'i' {
+				goto fraction
+			}
+			// octal int
+			if seenDecimalDigit {
+				s.error(offs, "illegal octal number")
+			}
+		}
+		return
+	}
+
+	// decimal int or float
+	s.scanMantissa(10)
+
+fraction:
+	if s.ch == '.' {
+		tok = token.Float
+		s.next()
+		s.scanMantissa(10)
+	}
+
+exponent:
+	if s.ch == 'e' || s.ch == 'E' {
+		tok = token.Float
+		s.next()
+		if s.ch == '-' || s.ch == '+' {
+			s.next()
+		}
+		if digitVal(s.ch) < 10 {
+			s.scanMantissa(10)
+		} else {
+			s.error(offs, "illegal floating-point exponent")
+		}
+	}
+	return
+}
+
+func (s *Scanner) scanEscape(quote rune) bool {
+	offs := s.offset
+
+	var n int
+	var base, max uint32
+	switch s.ch {
+	case 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', quote:
+		s.next()
+		return true
+	case '0', '1', '2', '3', '4', '5', '6', '7':
+		n, base, max = 3, 8, 255
+	case 'x':
+		s.next()
+		n, base, max = 2, 16, 255
+	case 'u':
+		s.next()
+		n, base, max = 4, 16, unicode.MaxRune
+	case 'U':
+		s.next()
+		n, base, max = 8, 16, unicode.MaxRune
+	default:
+		msg := "unknown escape sequence"
+		if s.ch < 0 {
+			msg = "escape sequence not terminated"
+		}
+		s.error(offs, msg)
+		return false
+	}
+
+	var x uint32
+	for n > 0 {
+		d := uint32(digitVal(s.ch))
+		if d >= base {
+			msg := fmt.Sprintf(
+				"illegal character %#U in escape sequence", s.ch)
+			if s.ch < 0 {
+				msg = "escape sequence not terminated"
+			}
+			s.error(s.offset, msg)
+			return false
+		}
+		x = x*base + d
+		s.next()
+		n--
+	}
+
+	if x > max || 0xD800 <= x && x < 0xE000 {
+		s.error(offs, "escape sequence is invalid Unicode code point")
+		return false
+	}
+	return true
+}
+
+func (s *Scanner) scanRune() string {
+	offs := s.offset - 1 // '\'' opening already consumed
+
+	valid := true
+	n := 0
+	for {
+		ch := s.ch
+		if ch == '\n' || ch < 0 {
+			// only report error if we don't have one already
+			if valid {
+				s.error(offs, "rune literal not terminated")
+				valid = false
+			}
+			break
+		}
+		s.next()
+		if ch == '\'' {
+			break
+		}
+		n++
+		if ch == '\\' {
+			if !s.scanEscape('\'') {
+				valid = false
+			}
+			// continue to read to closing quote
+		}
+	}
+
+	if valid && n != 1 {
+		s.error(offs, "illegal rune literal")
+	}
+	return string(s.src[offs:s.offset])
+}
+
+func (s *Scanner) scanString() string {
+	offs := s.offset - 1 // '"' opening already consumed
+
+	for {
+		ch := s.ch
+		if ch == '\n' || ch < 0 {
+			s.error(offs, "string literal not terminated")
+			break
+		}
+		s.next()
+		if ch == '"' {
+			break
+		}
+		if ch == '\\' {
+			s.scanEscape('"')
+		}
+	}
+	return string(s.src[offs:s.offset])
+}
+
+func (s *Scanner) scanRawString() string {
+	offs := s.offset - 1 // '`' opening already consumed
+
+	hasCR := false
+	for {
+		ch := s.ch
+		if ch < 0 {
+			s.error(offs, "raw string literal not terminated")
+			break
+		}
+
+		s.next()
+
+		if ch == '`' {
+			break
+		}
+
+		if ch == '\r' {
+			hasCR = true
+		}
+	}
+
+	lit := s.src[offs:s.offset]
+	if hasCR {
+		lit = StripCR(lit, false)
+	}
+	return string(lit)
+}
+
+// StripCR removes carriage return characters.
+func StripCR(b []byte, comment bool) []byte {
+	c := make([]byte, len(b))
+	i := 0
+	for j, ch := range b {
+		// In a /*-style comment, don't strip \r from *\r/ (incl. sequences of
+		// \r from *\r\r...\r/) since the resulting  */ would terminate the
+		// comment too early unless the \r is immediately following the opening
+		// /* in which case it's ok because /*/ is not closed yet.
+		if ch != '\r' || comment && i > len("/*") && c[i-1] == '*' &&
+			j+1 < len(b) && b[j+1] == '/' {
+			c[i] = ch
+			i++
+		}
+	}
+	return c[:i]
+}
+
+func (s *Scanner) skipWhitespace() {
+	for s.ch == ' ' || s.ch == '\t' || s.ch == '\n' && !s.insertSemi ||
+		s.ch == '\r' {
+		s.next()
+	}
+}
+
+func (s *Scanner) switch2(tok0, tok1 token.Token) token.Token {
+	if s.ch == '=' {
+		s.next()
+		return tok1
+	}
+	return tok0
+}
+
+func (s *Scanner) switch3(
+	tok0, tok1 token.Token,
+	ch2 rune,
+	tok2 token.Token,
+) token.Token {
+	if s.ch == '=' {
+		s.next()
+		return tok1
+	}
+	if s.ch == ch2 {
+		s.next()
+		return tok2
+	}
+	return tok0
+}
+
+func (s *Scanner) switch4(
+	tok0, tok1 token.Token,
+	ch2 rune,
+	tok2, tok3 token.Token,
+) token.Token {
+	if s.ch == '=' {
+		s.next()
+		return tok1
+	}
+	if s.ch == ch2 {
+		s.next()
+		if s.ch == '=' {
+			s.next()
+			return tok3
+		}
+		return tok2
+	}
+	return tok0
+}
+
+func isLetter(ch rune) bool {
+	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' ||
+		ch >= utf8.RuneSelf && unicode.IsLetter(ch)
+}
+
+func isDigit(ch rune) bool {
+	return '0' <= ch && ch <= '9' ||
+		ch >= utf8.RuneSelf && unicode.IsDigit(ch)
+}
+
+func digitVal(ch rune) int {
+	switch {
+	case '0' <= ch && ch <= '9':
+		return int(ch - '0')
+	case 'a' <= ch && ch <= 'f':
+		return int(ch - 'a' + 10)
+	case 'A' <= ch && ch <= 'F':
+		return int(ch - 'A' + 10)
+	}
+	return 16 // larger than any legal digit val
+}
diff --git a/vendor/github.com/d5/tengo/v2/parser/source_file.go b/vendor/github.com/d5/tengo/v2/parser/source_file.go
new file mode 100644
index 00000000..e9f4b0f5
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/parser/source_file.go
@@ -0,0 +1,231 @@
+package parser
+
+import (
+	"fmt"
+	"sort"
+)
+
+// SourceFilePos represents a position information in the file.
+type SourceFilePos struct {
+	Filename string // filename, if any
+	Offset   int    // offset, starting at 0
+	Line     int    // line number, starting at 1
+	Column   int    // column number, starting at 1 (byte count)
+}
+
+// IsValid returns true if the position is valid.
+func (p SourceFilePos) IsValid() bool {
+	return p.Line > 0
+}
+
+// String returns a string in one of several forms:
+//
+//	file:line:column    valid position with file name
+//	file:line           valid position with file name but no column (column == 0)
+//	line:column         valid position without file name
+//	line                valid position without file name and no column (column == 0)
+//	file                invalid position with file name
+//	-                   invalid position without file name
+//
+func (p SourceFilePos) String() string {
+	s := p.Filename
+	if p.IsValid() {
+		if s != "" {
+			s += ":"
+		}
+		s += fmt.Sprintf("%d", p.Line)
+		if p.Column != 0 {
+			s += fmt.Sprintf(":%d", p.Column)
+		}
+	}
+	if s == "" {
+		s = "-"
+	}
+	return s
+}
+
+// SourceFileSet represents a set of source files.
+type SourceFileSet struct {
+	Base     int           // base offset for the next file
+	Files    []*SourceFile // list of files in the order added to the set
+	LastFile *SourceFile   // cache of last file looked up
+}
+
+// NewFileSet creates a new file set.
+func NewFileSet() *SourceFileSet {
+	return &SourceFileSet{
+		Base: 1, // 0 == NoPos
+	}
+}
+
+// AddFile adds a new file in the file set.
+func (s *SourceFileSet) AddFile(filename string, base, size int) *SourceFile {
+	if base < 0 {
+		base = s.Base
+	}
+	if base < s.Base || size < 0 {
+		panic("illegal base or size")
+	}
+	f := &SourceFile{
+		set:   s,
+		Name:  filename,
+		Base:  base,
+		Size:  size,
+		Lines: []int{0},
+	}
+	base += size + 1 // +1 because EOF also has a position
+	if base < 0 {
+		panic("offset overflow (> 2G of source code in file set)")
+	}
+
+	// add the file to the file set
+	s.Base = base
+	s.Files = append(s.Files, f)
+	s.LastFile = f
+	return f
+}
+
+// File returns the file that contains the position p. If no such file is
+// found (for instance for p == NoPos), the result is nil.
+func (s *SourceFileSet) File(p Pos) (f *SourceFile) {
+	if p != NoPos {
+		f = s.file(p)
+	}
+	return
+}
+
+// Position converts a SourcePos p in the fileset into a SourceFilePos value.
+func (s *SourceFileSet) Position(p Pos) (pos SourceFilePos) {
+	if p != NoPos {
+		if f := s.file(p); f != nil {
+			return f.position(p)
+		}
+	}
+	return
+}
+
+func (s *SourceFileSet) file(p Pos) *SourceFile {
+	// common case: p is in last file
+	f := s.LastFile
+	if f != nil && f.Base <= int(p) && int(p) <= f.Base+f.Size {
+		return f
+	}
+
+	// p is not in last file - search all files
+	if i := searchFiles(s.Files, int(p)); i >= 0 {
+		f := s.Files[i]
+
+		// f.base <= int(p) by definition of searchFiles
+		if int(p) <= f.Base+f.Size {
+			s.LastFile = f // race is ok - s.last is only a cache
+			return f
+		}
+	}
+	return nil
+}
+
+func searchFiles(a []*SourceFile, x int) int {
+	return sort.Search(len(a), func(i int) bool { return a[i].Base > x }) - 1
+}
+
+// SourceFile represents a source file.
+type SourceFile struct {
+	// SourceFile set for the file
+	set *SourceFileSet
+	// SourceFile name as provided to AddFile
+	Name string
+	// SourcePos value range for this file is [base...base+size]
+	Base int
+	// SourceFile size as provided to AddFile
+	Size int
+	// Lines contains the offset of the first character for each line
+	// (the first entry is always 0)
+	Lines []int
+}
+
+// Set returns SourceFileSet.
+func (f *SourceFile) Set() *SourceFileSet {
+	return f.set
+}
+
+// LineCount returns the current number of lines.
+func (f *SourceFile) LineCount() int {
+	return len(f.Lines)
+}
+
+// AddLine adds a new line.
+func (f *SourceFile) AddLine(offset int) {
+	i := len(f.Lines)
+	if (i == 0 || f.Lines[i-1] < offset) && offset < f.Size {
+		f.Lines = append(f.Lines, offset)
+	}
+}
+
+// LineStart returns the position of the first character in the line.
+func (f *SourceFile) LineStart(line int) Pos {
+	if line < 1 {
+		panic("illegal line number (line numbering starts at 1)")
+	}
+	if line > len(f.Lines) {
+		panic("illegal line number")
+	}
+	return Pos(f.Base + f.Lines[line-1])
+}
+
+// FileSetPos returns the position in the file set.
+func (f *SourceFile) FileSetPos(offset int) Pos {
+	if offset > f.Size {
+		panic("illegal file offset")
+	}
+	return Pos(f.Base + offset)
+}
+
+// Offset translates the file set position into the file offset.
+func (f *SourceFile) Offset(p Pos) int {
+	if int(p) < f.Base || int(p) > f.Base+f.Size {
+		panic("illegal SourcePos value")
+	}
+	return int(p) - f.Base
+}
+
+// Position translates the file set position into the file position.
+func (f *SourceFile) Position(p Pos) (pos SourceFilePos) {
+	if p != NoPos {
+		if int(p) < f.Base || int(p) > f.Base+f.Size {
+			panic("illegal SourcePos value")
+		}
+		pos = f.position(p)
+	}
+	return
+}
+
+func (f *SourceFile) position(p Pos) (pos SourceFilePos) {
+	offset := int(p) - f.Base
+	pos.Offset = offset
+	pos.Filename, pos.Line, pos.Column = f.unpack(offset)
+	return
+}
+
+func (f *SourceFile) unpack(offset int) (filename string, line, column int) {
+	filename = f.Name
+	if i := searchInts(f.Lines, offset); i >= 0 {
+		line, column = i+1, offset-f.Lines[i]+1
+	}
+	return
+}
+
+func searchInts(a []int, x int) int {
+	// This function body is a manually inlined version of:
+	//   return sort.Search(len(a), func(i int) bool { return a[i] > x }) - 1
+	i, j := 0, len(a)
+	for i < j {
+		h := i + (j-i)/2 // avoid overflow when computing h
+		// i ≤ h < j
+		if a[h] <= x {
+			i = h + 1
+		} else {
+			j = h
+		}
+	}
+	return i - 1
+}
diff --git a/vendor/github.com/d5/tengo/v2/parser/stmt.go b/vendor/github.com/d5/tengo/v2/parser/stmt.go
new file mode 100644
index 00000000..c0848c48
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/parser/stmt.go
@@ -0,0 +1,349 @@
+package parser
+
+import (
+	"strings"
+
+	"github.com/d5/tengo/v2/token"
+)
+
+// Stmt represents a statement in the AST.
+type Stmt interface {
+	Node
+	stmtNode()
+}
+
+// AssignStmt represents an assignment statement.
+type AssignStmt struct {
+	LHS      []Expr
+	RHS      []Expr
+	Token    token.Token
+	TokenPos Pos
+}
+
+func (s *AssignStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *AssignStmt) Pos() Pos {
+	return s.LHS[0].Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (s *AssignStmt) End() Pos {
+	return s.RHS[len(s.RHS)-1].End()
+}
+
+func (s *AssignStmt) String() string {
+	var lhs, rhs []string
+	for _, e := range s.LHS {
+		lhs = append(lhs, e.String())
+	}
+	for _, e := range s.RHS {
+		rhs = append(rhs, e.String())
+	}
+	return strings.Join(lhs, ", ") + " " + s.Token.String() +
+		" " + strings.Join(rhs, ", ")
+}
+
+// BadStmt represents a bad statement.
+type BadStmt struct {
+	From Pos
+	To   Pos
+}
+
+func (s *BadStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *BadStmt) Pos() Pos {
+	return s.From
+}
+
+// End returns the position of first character immediately after the node.
+func (s *BadStmt) End() Pos {
+	return s.To
+}
+
+func (s *BadStmt) String() string {
+	return "<bad statement>"
+}
+
+// BlockStmt represents a block statement.
+type BlockStmt struct {
+	Stmts  []Stmt
+	LBrace Pos
+	RBrace Pos
+}
+
+func (s *BlockStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *BlockStmt) Pos() Pos {
+	return s.LBrace
+}
+
+// End returns the position of first character immediately after the node.
+func (s *BlockStmt) End() Pos {
+	return s.RBrace + 1
+}
+
+func (s *BlockStmt) String() string {
+	var list []string
+	for _, e := range s.Stmts {
+		list = append(list, e.String())
+	}
+	return "{" + strings.Join(list, "; ") + "}"
+}
+
+// BranchStmt represents a branch statement.
+type BranchStmt struct {
+	Token    token.Token
+	TokenPos Pos
+	Label    *Ident
+}
+
+func (s *BranchStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *BranchStmt) Pos() Pos {
+	return s.TokenPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *BranchStmt) End() Pos {
+	if s.Label != nil {
+		return s.Label.End()
+	}
+
+	return Pos(int(s.TokenPos) + len(s.Token.String()))
+}
+
+func (s *BranchStmt) String() string {
+	var label string
+	if s.Label != nil {
+		label = " " + s.Label.Name
+	}
+	return s.Token.String() + label
+}
+
+// EmptyStmt represents an empty statement.
+type EmptyStmt struct {
+	Semicolon Pos
+	Implicit  bool
+}
+
+func (s *EmptyStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *EmptyStmt) Pos() Pos {
+	return s.Semicolon
+}
+
+// End returns the position of first character immediately after the node.
+func (s *EmptyStmt) End() Pos {
+	if s.Implicit {
+		return s.Semicolon
+	}
+	return s.Semicolon + 1
+}
+
+func (s *EmptyStmt) String() string {
+	return ";"
+}
+
+// ExportStmt represents an export statement.
+type ExportStmt struct {
+	ExportPos Pos
+	Result    Expr
+}
+
+func (s *ExportStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *ExportStmt) Pos() Pos {
+	return s.ExportPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ExportStmt) End() Pos {
+	return s.Result.End()
+}
+
+func (s *ExportStmt) String() string {
+	return "export " + s.Result.String()
+}
+
+// ExprStmt represents an expression statement.
+type ExprStmt struct {
+	Expr Expr
+}
+
+func (s *ExprStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *ExprStmt) Pos() Pos {
+	return s.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ExprStmt) End() Pos {
+	return s.Expr.End()
+}
+
+func (s *ExprStmt) String() string {
+	return s.Expr.String()
+}
+
+// ForInStmt represents a for-in statement.
+type ForInStmt struct {
+	ForPos   Pos
+	Key      *Ident
+	Value    *Ident
+	Iterable Expr
+	Body     *BlockStmt
+}
+
+func (s *ForInStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *ForInStmt) Pos() Pos {
+	return s.ForPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ForInStmt) End() Pos {
+	return s.Body.End()
+}
+
+func (s *ForInStmt) String() string {
+	if s.Value != nil {
+		return "for " + s.Key.String() + ", " + s.Value.String() +
+			" in " + s.Iterable.String() + " " + s.Body.String()
+	}
+	return "for " + s.Key.String() + " in " + s.Iterable.String() +
+		" " + s.Body.String()
+}
+
+// ForStmt represents a for statement.
+type ForStmt struct {
+	ForPos Pos
+	Init   Stmt
+	Cond   Expr
+	Post   Stmt
+	Body   *BlockStmt
+}
+
+func (s *ForStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *ForStmt) Pos() Pos {
+	return s.ForPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ForStmt) End() Pos {
+	return s.Body.End()
+}
+
+func (s *ForStmt) String() string {
+	var init, cond, post string
+	if s.Init != nil {
+		init = s.Init.String()
+	}
+	if s.Cond != nil {
+		cond = s.Cond.String() + " "
+	}
+	if s.Post != nil {
+		post = s.Post.String()
+	}
+
+	if init != "" || post != "" {
+		return "for " + init + " ; " + cond + " ; " + post + s.Body.String()
+	}
+	return "for " + cond + s.Body.String()
+}
+
+// IfStmt represents an if statement.
+type IfStmt struct {
+	IfPos Pos
+	Init  Stmt
+	Cond  Expr
+	Body  *BlockStmt
+	Else  Stmt // else branch; or nil
+}
+
+func (s *IfStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *IfStmt) Pos() Pos {
+	return s.IfPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *IfStmt) End() Pos {
+	if s.Else != nil {
+		return s.Else.End()
+	}
+	return s.Body.End()
+}
+
+func (s *IfStmt) String() string {
+	var initStmt, elseStmt string
+	if s.Init != nil {
+		initStmt = s.Init.String() + "; "
+	}
+	if s.Else != nil {
+		elseStmt = " else " + s.Else.String()
+	}
+	return "if " + initStmt + s.Cond.String() + " " +
+		s.Body.String() + elseStmt
+}
+
+// IncDecStmt represents increment or decrement statement.
+type IncDecStmt struct {
+	Expr     Expr
+	Token    token.Token
+	TokenPos Pos
+}
+
+func (s *IncDecStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *IncDecStmt) Pos() Pos {
+	return s.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (s *IncDecStmt) End() Pos {
+	return Pos(int(s.TokenPos) + 2)
+}
+
+func (s *IncDecStmt) String() string {
+	return s.Expr.String() + s.Token.String()
+}
+
+// ReturnStmt represents a return statement.
+type ReturnStmt struct {
+	ReturnPos Pos
+	Result    Expr
+}
+
+func (s *ReturnStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *ReturnStmt) Pos() Pos {
+	return s.ReturnPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ReturnStmt) End() Pos {
+	if s.Result != nil {
+		return s.Result.End()
+	}
+	return s.ReturnPos + 6
+}
+
+func (s *ReturnStmt) String() string {
+	if s.Result != nil {
+		return "return " + s.Result.String()
+	}
+	return "return"
+}
diff --git a/vendor/github.com/d5/tengo/v2/script.go b/vendor/github.com/d5/tengo/v2/script.go
new file mode 100644
index 00000000..906771d9
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/script.go
@@ -0,0 +1,313 @@
+package tengo
+
+import (
+	"context"
+	"fmt"
+	"sync"
+
+	"github.com/d5/tengo/v2/parser"
+)
+
+// Script can simplify compilation and execution of embedded scripts.
+type Script struct {
+	variables        map[string]*Variable
+	modules          *ModuleMap
+	input            []byte
+	maxAllocs        int64
+	maxConstObjects  int
+	enableFileImport bool
+}
+
+// NewScript creates a Script instance with an input script.
+func NewScript(input []byte) *Script {
+	return &Script{
+		variables:       make(map[string]*Variable),
+		input:           input,
+		maxAllocs:       -1,
+		maxConstObjects: -1,
+	}
+}
+
+// Add adds a new variable or updates an existing variable to the script.
+func (s *Script) Add(name string, value interface{}) error {
+	obj, err := FromInterface(value)
+	if err != nil {
+		return err
+	}
+	s.variables[name] = &Variable{
+		name:  name,
+		value: obj,
+	}
+	return nil
+}
+
+// Remove removes (undefines) an existing variable for the script. It returns
+// false if the variable name is not defined.
+func (s *Script) Remove(name string) bool {
+	if _, ok := s.variables[name]; !ok {
+		return false
+	}
+	delete(s.variables, name)
+	return true
+}
+
+// SetImports sets import modules.
+func (s *Script) SetImports(modules *ModuleMap) {
+	s.modules = modules
+}
+
+// SetMaxAllocs sets the maximum number of objects allocations during the run
+// time. Compiled script will return ErrObjectAllocLimit error if it
+// exceeds this limit.
+func (s *Script) SetMaxAllocs(n int64) {
+	s.maxAllocs = n
+}
+
+// SetMaxConstObjects sets the maximum number of objects in the compiled
+// constants.
+func (s *Script) SetMaxConstObjects(n int) {
+	s.maxConstObjects = n
+}
+
+// EnableFileImport enables or disables module loading from local files. Local
+// file modules are disabled by default.
+func (s *Script) EnableFileImport(enable bool) {
+	s.enableFileImport = enable
+}
+
+// Compile compiles the script with all the defined variables, and, returns
+// Compiled object.
+func (s *Script) Compile() (*Compiled, error) {
+	symbolTable, globals, err := s.prepCompile()
+	if err != nil {
+		return nil, err
+	}
+
+	fileSet := parser.NewFileSet()
+	srcFile := fileSet.AddFile("(main)", -1, len(s.input))
+	p := parser.NewParser(srcFile, s.input, nil)
+	file, err := p.ParseFile()
+	if err != nil {
+		return nil, err
+	}
+
+	c := NewCompiler(srcFile, symbolTable, nil, s.modules, nil)
+	c.EnableFileImport(s.enableFileImport)
+	if err := c.Compile(file); err != nil {
+		return nil, err
+	}
+
+	// reduce globals size
+	globals = globals[:symbolTable.MaxSymbols()+1]
+
+	// global symbol names to indexes
+	globalIndexes := make(map[string]int, len(globals))
+	for _, name := range symbolTable.Names() {
+		symbol, _, _ := symbolTable.Resolve(name)
+		if symbol.Scope == ScopeGlobal {
+			globalIndexes[name] = symbol.Index
+		}
+	}
+
+	// remove duplicates from constants
+	bytecode := c.Bytecode()
+	bytecode.RemoveDuplicates()
+
+	// check the constant objects limit
+	if s.maxConstObjects >= 0 {
+		cnt := bytecode.CountObjects()
+		if cnt > s.maxConstObjects {
+			return nil, fmt.Errorf("exceeding constant objects limit: %d", cnt)
+		}
+	}
+	return &Compiled{
+		globalIndexes: globalIndexes,
+		bytecode:      bytecode,
+		globals:       globals,
+		maxAllocs:     s.maxAllocs,
+	}, nil
+}
+
+// Run compiles and runs the scripts. Use returned compiled object to access
+// global variables.
+func (s *Script) Run() (compiled *Compiled, err error) {
+	compiled, err = s.Compile()
+	if err != nil {
+		return
+	}
+	err = compiled.Run()
+	return
+}
+
+// RunContext is like Run but includes a context.
+func (s *Script) RunContext(
+	ctx context.Context,
+) (compiled *Compiled, err error) {
+	compiled, err = s.Compile()
+	if err != nil {
+		return
+	}
+	err = compiled.RunContext(ctx)
+	return
+}
+
+func (s *Script) prepCompile() (
+	symbolTable *SymbolTable,
+	globals []Object,
+	err error,
+) {
+	var names []string
+	for name := range s.variables {
+		names = append(names, name)
+	}
+
+	symbolTable = NewSymbolTable()
+	for idx, fn := range builtinFuncs {
+		symbolTable.DefineBuiltin(idx, fn.Name)
+	}
+
+	globals = make([]Object, GlobalsSize)
+
+	for idx, name := range names {
+		symbol := symbolTable.Define(name)
+		if symbol.Index != idx {
+			panic(fmt.Errorf("wrong symbol index: %d != %d",
+				idx, symbol.Index))
+		}
+		globals[symbol.Index] = s.variables[name].value
+	}
+	return
+}
+
+// Compiled is a compiled instance of the user script. Use Script.Compile() to
+// create Compiled object.
+type Compiled struct {
+	globalIndexes map[string]int // global symbol name to index
+	bytecode      *Bytecode
+	globals       []Object
+	maxAllocs     int64
+	lock          sync.RWMutex
+}
+
+// Run executes the compiled script in the virtual machine.
+func (c *Compiled) Run() error {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	v := NewVM(c.bytecode, c.globals, c.maxAllocs)
+	return v.Run()
+}
+
+// RunContext is like Run but includes a context.
+func (c *Compiled) RunContext(ctx context.Context) (err error) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	v := NewVM(c.bytecode, c.globals, c.maxAllocs)
+	ch := make(chan error, 1)
+	go func() {
+		ch <- v.Run()
+	}()
+
+	select {
+	case <-ctx.Done():
+		v.Abort()
+		<-ch
+		err = ctx.Err()
+	case err = <-ch:
+	}
+	return
+}
+
+// Clone creates a new copy of Compiled. Cloned copies are safe for concurrent
+// use by multiple goroutines.
+func (c *Compiled) Clone() *Compiled {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	clone := &Compiled{
+		globalIndexes: c.globalIndexes,
+		bytecode:      c.bytecode,
+		globals:       make([]Object, len(c.globals)),
+		maxAllocs:     c.maxAllocs,
+	}
+	// copy global objects
+	for idx, g := range c.globals {
+		if g != nil {
+			clone.globals[idx] = g
+		}
+	}
+	return clone
+}
+
+// IsDefined returns true if the variable name is defined (has value) before or
+// after the execution.
+func (c *Compiled) IsDefined(name string) bool {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+
+	idx, ok := c.globalIndexes[name]
+	if !ok {
+		return false
+	}
+	v := c.globals[idx]
+	if v == nil {
+		return false
+	}
+	return v != UndefinedValue
+}
+
+// Get returns a variable identified by the name.
+func (c *Compiled) Get(name string) *Variable {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+
+	value := UndefinedValue
+	if idx, ok := c.globalIndexes[name]; ok {
+		value = c.globals[idx]
+		if value == nil {
+			value = UndefinedValue
+		}
+	}
+	return &Variable{
+		name:  name,
+		value: value,
+	}
+}
+
+// GetAll returns all the variables that are defined by the compiled script.
+func (c *Compiled) GetAll() []*Variable {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+
+	var vars []*Variable
+	for name, idx := range c.globalIndexes {
+		value := c.globals[idx]
+		if value == nil {
+			value = UndefinedValue
+		}
+		vars = append(vars, &Variable{
+			name:  name,
+			value: value,
+		})
+	}
+	return vars
+}
+
+// Set replaces the value of a global variable identified by the name. An error
+// will be returned if the name was not defined during compilation.
+func (c *Compiled) Set(name string, value interface{}) error {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	obj, err := FromInterface(value)
+	if err != nil {
+		return err
+	}
+	idx, ok := c.globalIndexes[name]
+	if !ok {
+		return fmt.Errorf("'%s' is not defined", name)
+	}
+	c.globals[idx] = obj
+	return nil
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/base64.go b/vendor/github.com/d5/tengo/v2/stdlib/base64.go
new file mode 100644
index 00000000..b4c5b56e
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/base64.go
@@ -0,0 +1,34 @@
+package stdlib
+
+import (
+	"encoding/base64"
+
+	"github.com/d5/tengo/v2"
+)
+
+var base64Module = map[string]tengo.Object{
+	"encode": &tengo.UserFunction{
+		Value: FuncAYRS(base64.StdEncoding.EncodeToString),
+	},
+	"decode": &tengo.UserFunction{
+		Value: FuncASRYE(base64.StdEncoding.DecodeString),
+	},
+	"raw_encode": &tengo.UserFunction{
+		Value: FuncAYRS(base64.RawStdEncoding.EncodeToString),
+	},
+	"raw_decode": &tengo.UserFunction{
+		Value: FuncASRYE(base64.RawStdEncoding.DecodeString),
+	},
+	"url_encode": &tengo.UserFunction{
+		Value: FuncAYRS(base64.URLEncoding.EncodeToString),
+	},
+	"url_decode": &tengo.UserFunction{
+		Value: FuncASRYE(base64.URLEncoding.DecodeString),
+	},
+	"raw_url_encode": &tengo.UserFunction{
+		Value: FuncAYRS(base64.RawURLEncoding.EncodeToString),
+	},
+	"raw_url_decode": &tengo.UserFunction{
+		Value: FuncASRYE(base64.RawURLEncoding.DecodeString),
+	},
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/builtin_modules.go b/vendor/github.com/d5/tengo/v2/stdlib/builtin_modules.go
new file mode 100644
index 00000000..cf0e9621
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/builtin_modules.go
@@ -0,0 +1,18 @@
+package stdlib
+
+import (
+	"github.com/d5/tengo/v2"
+)
+
+// BuiltinModules are builtin type standard library modules.
+var BuiltinModules = map[string]map[string]tengo.Object{
+	"math":   mathModule,
+	"os":     osModule,
+	"text":   textModule,
+	"times":  timesModule,
+	"rand":   randModule,
+	"fmt":    fmtModule,
+	"json":   jsonModule,
+	"base64": base64Module,
+	"hex":    hexModule,
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/errors.go b/vendor/github.com/d5/tengo/v2/stdlib/errors.go
new file mode 100644
index 00000000..ad83c6f8
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/errors.go
@@ -0,0 +1,12 @@
+package stdlib
+
+import (
+	"github.com/d5/tengo/v2"
+)
+
+func wrapError(err error) tengo.Object {
+	if err == nil {
+		return tengo.TrueValue
+	}
+	return &tengo.Error{Value: &tengo.String{Value: err.Error()}}
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/fmt.go b/vendor/github.com/d5/tengo/v2/stdlib/fmt.go
new file mode 100644
index 00000000..9945277f
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/fmt.go
@@ -0,0 +1,101 @@
+package stdlib
+
+import (
+	"fmt"
+
+	"github.com/d5/tengo/v2"
+)
+
+var fmtModule = map[string]tengo.Object{
+	"print":   &tengo.UserFunction{Name: "print", Value: fmtPrint},
+	"printf":  &tengo.UserFunction{Name: "printf", Value: fmtPrintf},
+	"println": &tengo.UserFunction{Name: "println", Value: fmtPrintln},
+	"sprintf": &tengo.UserFunction{Name: "sprintf", Value: fmtSprintf},
+}
+
+func fmtPrint(args ...tengo.Object) (ret tengo.Object, err error) {
+	printArgs, err := getPrintArgs(args...)
+	if err != nil {
+		return nil, err
+	}
+	_, _ = fmt.Print(printArgs...)
+	return nil, nil
+}
+
+func fmtPrintf(args ...tengo.Object) (ret tengo.Object, err error) {
+	numArgs := len(args)
+	if numArgs == 0 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+
+	format, ok := args[0].(*tengo.String)
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "format",
+			Expected: "string",
+			Found:    args[0].TypeName(),
+		}
+	}
+	if numArgs == 1 {
+		fmt.Print(format)
+		return nil, nil
+	}
+
+	s, err := tengo.Format(format.Value, args[1:]...)
+	if err != nil {
+		return nil, err
+	}
+	fmt.Print(s)
+	return nil, nil
+}
+
+func fmtPrintln(args ...tengo.Object) (ret tengo.Object, err error) {
+	printArgs, err := getPrintArgs(args...)
+	if err != nil {
+		return nil, err
+	}
+	printArgs = append(printArgs, "\n")
+	_, _ = fmt.Print(printArgs...)
+	return nil, nil
+}
+
+func fmtSprintf(args ...tengo.Object) (ret tengo.Object, err error) {
+	numArgs := len(args)
+	if numArgs == 0 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+
+	format, ok := args[0].(*tengo.String)
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "format",
+			Expected: "string",
+			Found:    args[0].TypeName(),
+		}
+	}
+	if numArgs == 1 {
+		// okay to return 'format' directly as String is immutable
+		return format, nil
+	}
+	s, err := tengo.Format(format.Value, args[1:]...)
+	if err != nil {
+		return nil, err
+	}
+	return &tengo.String{Value: s}, nil
+}
+
+func getPrintArgs(args ...tengo.Object) ([]interface{}, error) {
+	var printArgs []interface{}
+	l := 0
+	for _, arg := range args {
+		s, _ := tengo.ToString(arg)
+		slen := len(s)
+		// make sure length does not exceed the limit
+		if l+slen > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		l += slen
+		printArgs = append(printArgs, s)
+	}
+	return printArgs, nil
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/func_typedefs.go b/vendor/github.com/d5/tengo/v2/stdlib/func_typedefs.go
new file mode 100644
index 00000000..fdac933c
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/func_typedefs.go
@@ -0,0 +1,1049 @@
+package stdlib
+
+import (
+	"fmt"
+
+	"github.com/d5/tengo/v2"
+)
+
+// FuncAR transform a function of 'func()' signature into CallableFunc type.
+func FuncAR(fn func()) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		fn()
+		return tengo.UndefinedValue, nil
+	}
+}
+
+// FuncARI transform a function of 'func() int' signature into CallableFunc
+// type.
+func FuncARI(fn func() int) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		return &tengo.Int{Value: int64(fn())}, nil
+	}
+}
+
+// FuncARI64 transform a function of 'func() int64' signature into CallableFunc
+// type.
+func FuncARI64(fn func() int64) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		return &tengo.Int{Value: fn()}, nil
+	}
+}
+
+// FuncAI64RI64 transform a function of 'func(int64) int64' signature into
+// CallableFunc type.
+func FuncAI64RI64(fn func(int64) int64) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+
+		i1, ok := tengo.ToInt64(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "int(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		return &tengo.Int{Value: fn(i1)}, nil
+	}
+}
+
+// FuncAI64R transform a function of 'func(int64)' signature into CallableFunc
+// type.
+func FuncAI64R(fn func(int64)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+
+		i1, ok := tengo.ToInt64(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "int(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		fn(i1)
+		return tengo.UndefinedValue, nil
+	}
+}
+
+// FuncARB transform a function of 'func() bool' signature into CallableFunc
+// type.
+func FuncARB(fn func() bool) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		if fn() {
+			return tengo.TrueValue, nil
+		}
+		return tengo.FalseValue, nil
+	}
+}
+
+// FuncARE transform a function of 'func() error' signature into CallableFunc
+// type.
+func FuncARE(fn func() error) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		return wrapError(fn()), nil
+	}
+}
+
+// FuncARS transform a function of 'func() string' signature into CallableFunc
+// type.
+func FuncARS(fn func() string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s := fn()
+		if len(s) > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		return &tengo.String{Value: s}, nil
+	}
+}
+
+// FuncARSE transform a function of 'func() (string, error)' signature into
+// CallableFunc type.
+func FuncARSE(fn func() (string, error)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		res, err := fn()
+		if err != nil {
+			return wrapError(err), nil
+		}
+		if len(res) > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		return &tengo.String{Value: res}, nil
+	}
+}
+
+// FuncARYE transform a function of 'func() ([]byte, error)' signature into
+// CallableFunc type.
+func FuncARYE(fn func() ([]byte, error)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		res, err := fn()
+		if err != nil {
+			return wrapError(err), nil
+		}
+		if len(res) > tengo.MaxBytesLen {
+			return nil, tengo.ErrBytesLimit
+		}
+		return &tengo.Bytes{Value: res}, nil
+	}
+}
+
+// FuncARF transform a function of 'func() float64' signature into CallableFunc
+// type.
+func FuncARF(fn func() float64) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		return &tengo.Float{Value: fn()}, nil
+	}
+}
+
+// FuncARSs transform a function of 'func() []string' signature into
+// CallableFunc type.
+func FuncARSs(fn func() []string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		arr := &tengo.Array{}
+		for _, elem := range fn() {
+			if len(elem) > tengo.MaxStringLen {
+				return nil, tengo.ErrStringLimit
+			}
+			arr.Value = append(arr.Value, &tengo.String{Value: elem})
+		}
+		return arr, nil
+	}
+}
+
+// FuncARIsE transform a function of 'func() ([]int, error)' signature into
+// CallableFunc type.
+func FuncARIsE(fn func() ([]int, error)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 0 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		res, err := fn()
+		if err != nil {
+			return wrapError(err), nil
+		}
+		arr := &tengo.Array{}
+		for _, v := range res {
+			arr.Value = append(arr.Value, &tengo.Int{Value: int64(v)})
+		}
+		return arr, nil
+	}
+}
+
+// FuncAIRIs transform a function of 'func(int) []int' signature into
+// CallableFunc type.
+func FuncAIRIs(fn func(int) []int) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		i1, ok := tengo.ToInt(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "int(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		res := fn(i1)
+		arr := &tengo.Array{}
+		for _, v := range res {
+			arr.Value = append(arr.Value, &tengo.Int{Value: int64(v)})
+		}
+		return arr, nil
+	}
+}
+
+// FuncAFRF transform a function of 'func(float64) float64' signature into
+// CallableFunc type.
+func FuncAFRF(fn func(float64) float64) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		f1, ok := tengo.ToFloat64(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "float(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		return &tengo.Float{Value: fn(f1)}, nil
+	}
+}
+
+// FuncAIR transform a function of 'func(int)' signature into CallableFunc type.
+func FuncAIR(fn func(int)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		i1, ok := tengo.ToInt(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "int(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		fn(i1)
+		return tengo.UndefinedValue, nil
+	}
+}
+
+// FuncAIRF transform a function of 'func(int) float64' signature into
+// CallableFunc type.
+func FuncAIRF(fn func(int) float64) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		i1, ok := tengo.ToInt(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "int(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		return &tengo.Float{Value: fn(i1)}, nil
+	}
+}
+
+// FuncAFRI transform a function of 'func(float64) int' signature into
+// CallableFunc type.
+func FuncAFRI(fn func(float64) int) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		f1, ok := tengo.ToFloat64(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "float(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		return &tengo.Int{Value: int64(fn(f1))}, nil
+	}
+}
+
+// FuncAFFRF transform a function of 'func(float64, float64) float64' signature
+// into CallableFunc type.
+func FuncAFFRF(fn func(float64, float64) float64) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		f1, ok := tengo.ToFloat64(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "float(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		f2, ok := tengo.ToFloat64(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "float(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		return &tengo.Float{Value: fn(f1, f2)}, nil
+	}
+}
+
+// FuncAIFRF transform a function of 'func(int, float64) float64' signature
+// into CallableFunc type.
+func FuncAIFRF(fn func(int, float64) float64) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		i1, ok := tengo.ToInt(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "int(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		f2, ok := tengo.ToFloat64(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "float(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		return &tengo.Float{Value: fn(i1, f2)}, nil
+	}
+}
+
+// FuncAFIRF transform a function of 'func(float64, int) float64' signature
+// into CallableFunc type.
+func FuncAFIRF(fn func(float64, int) float64) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		f1, ok := tengo.ToFloat64(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "float(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		i2, ok := tengo.ToInt(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "int(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		return &tengo.Float{Value: fn(f1, i2)}, nil
+	}
+}
+
+// FuncAFIRB transform a function of 'func(float64, int) bool' signature
+// into CallableFunc type.
+func FuncAFIRB(fn func(float64, int) bool) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		f1, ok := tengo.ToFloat64(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "float(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		i2, ok := tengo.ToInt(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "int(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		if fn(f1, i2) {
+			return tengo.TrueValue, nil
+		}
+		return tengo.FalseValue, nil
+	}
+}
+
+// FuncAFRB transform a function of 'func(float64) bool' signature
+// into CallableFunc type.
+func FuncAFRB(fn func(float64) bool) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		f1, ok := tengo.ToFloat64(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "float(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		if fn(f1) {
+			return tengo.TrueValue, nil
+		}
+		return tengo.FalseValue, nil
+	}
+}
+
+// FuncASRS transform a function of 'func(string) string' signature into
+// CallableFunc type. User function will return 'true' if underlying native
+// function returns nil.
+func FuncASRS(fn func(string) string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		s := fn(s1)
+		if len(s) > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		return &tengo.String{Value: s}, nil
+	}
+}
+
+// FuncASRSs transform a function of 'func(string) []string' signature into
+// CallableFunc type.
+func FuncASRSs(fn func(string) []string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		res := fn(s1)
+		arr := &tengo.Array{}
+		for _, elem := range res {
+			if len(elem) > tengo.MaxStringLen {
+				return nil, tengo.ErrStringLimit
+			}
+			arr.Value = append(arr.Value, &tengo.String{Value: elem})
+		}
+		return arr, nil
+	}
+}
+
+// FuncASRSE transform a function of 'func(string) (string, error)' signature
+// into CallableFunc type. User function will return 'true' if underlying
+// native function returns nil.
+func FuncASRSE(fn func(string) (string, error)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		res, err := fn(s1)
+		if err != nil {
+			return wrapError(err), nil
+		}
+		if len(res) > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		return &tengo.String{Value: res}, nil
+	}
+}
+
+// FuncASRE transform a function of 'func(string) error' signature into
+// CallableFunc type. User function will return 'true' if underlying native
+// function returns nil.
+func FuncASRE(fn func(string) error) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		return wrapError(fn(s1)), nil
+	}
+}
+
+// FuncASSRE transform a function of 'func(string, string) error' signature
+// into CallableFunc type. User function will return 'true' if underlying
+// native function returns nil.
+func FuncASSRE(fn func(string, string) error) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		s2, ok := tengo.ToString(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "string(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		return wrapError(fn(s1, s2)), nil
+	}
+}
+
+// FuncASSRSs transform a function of 'func(string, string) []string'
+// signature into CallableFunc type.
+func FuncASSRSs(fn func(string, string) []string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		s2, ok := tengo.ToString(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		arr := &tengo.Array{}
+		for _, res := range fn(s1, s2) {
+			if len(res) > tengo.MaxStringLen {
+				return nil, tengo.ErrStringLimit
+			}
+			arr.Value = append(arr.Value, &tengo.String{Value: res})
+		}
+		return arr, nil
+	}
+}
+
+// FuncASSIRSs transform a function of 'func(string, string, int) []string'
+// signature into CallableFunc type.
+func FuncASSIRSs(fn func(string, string, int) []string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 3 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		s2, ok := tengo.ToString(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "string(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		i3, ok := tengo.ToInt(args[2])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "third",
+				Expected: "int(compatible)",
+				Found:    args[2].TypeName(),
+			}
+		}
+		arr := &tengo.Array{}
+		for _, res := range fn(s1, s2, i3) {
+			if len(res) > tengo.MaxStringLen {
+				return nil, tengo.ErrStringLimit
+			}
+			arr.Value = append(arr.Value, &tengo.String{Value: res})
+		}
+		return arr, nil
+	}
+}
+
+// FuncASSRI transform a function of 'func(string, string) int' signature into
+// CallableFunc type.
+func FuncASSRI(fn func(string, string) int) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		s2, ok := tengo.ToString(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		return &tengo.Int{Value: int64(fn(s1, s2))}, nil
+	}
+}
+
+// FuncASSRS transform a function of 'func(string, string) string' signature
+// into CallableFunc type.
+func FuncASSRS(fn func(string, string) string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		s2, ok := tengo.ToString(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "string(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		s := fn(s1, s2)
+		if len(s) > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		return &tengo.String{Value: s}, nil
+	}
+}
+
+// FuncASSRB transform a function of 'func(string, string) bool' signature
+// into CallableFunc type.
+func FuncASSRB(fn func(string, string) bool) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		s2, ok := tengo.ToString(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "string(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		if fn(s1, s2) {
+			return tengo.TrueValue, nil
+		}
+		return tengo.FalseValue, nil
+	}
+}
+
+// FuncASsSRS transform a function of 'func([]string, string) string' signature
+// into CallableFunc type.
+func FuncASsSRS(fn func([]string, string) string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (tengo.Object, error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		var ss1 []string
+		switch arg0 := args[0].(type) {
+		case *tengo.Array:
+			for idx, a := range arg0.Value {
+				as, ok := tengo.ToString(a)
+				if !ok {
+					return nil, tengo.ErrInvalidArgumentType{
+						Name:     fmt.Sprintf("first[%d]", idx),
+						Expected: "string(compatible)",
+						Found:    a.TypeName(),
+					}
+				}
+				ss1 = append(ss1, as)
+			}
+		case *tengo.ImmutableArray:
+			for idx, a := range arg0.Value {
+				as, ok := tengo.ToString(a)
+				if !ok {
+					return nil, tengo.ErrInvalidArgumentType{
+						Name:     fmt.Sprintf("first[%d]", idx),
+						Expected: "string(compatible)",
+						Found:    a.TypeName(),
+					}
+				}
+				ss1 = append(ss1, as)
+			}
+		default:
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "array",
+				Found:    args[0].TypeName(),
+			}
+		}
+		s2, ok := tengo.ToString(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "string(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		s := fn(ss1, s2)
+		if len(s) > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		return &tengo.String{Value: s}, nil
+	}
+}
+
+// FuncASI64RE transform a function of 'func(string, int64) error' signature
+// into CallableFunc type.
+func FuncASI64RE(fn func(string, int64) error) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		i2, ok := tengo.ToInt64(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "int(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		return wrapError(fn(s1, i2)), nil
+	}
+}
+
+// FuncAIIRE transform a function of 'func(int, int) error' signature
+// into CallableFunc type.
+func FuncAIIRE(fn func(int, int) error) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		i1, ok := tengo.ToInt(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "int(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		i2, ok := tengo.ToInt(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "int(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		return wrapError(fn(i1, i2)), nil
+	}
+}
+
+// FuncASIRS transform a function of 'func(string, int) string' signature
+// into CallableFunc type.
+func FuncASIRS(fn func(string, int) string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 2 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		i2, ok := tengo.ToInt(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "int(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		s := fn(s1, i2)
+		if len(s) > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		return &tengo.String{Value: s}, nil
+	}
+}
+
+// FuncASIIRE transform a function of 'func(string, int, int) error' signature
+// into CallableFunc type.
+func FuncASIIRE(fn func(string, int, int) error) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 3 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		i2, ok := tengo.ToInt(args[1])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "second",
+				Expected: "int(compatible)",
+				Found:    args[1].TypeName(),
+			}
+		}
+		i3, ok := tengo.ToInt(args[2])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "third",
+				Expected: "int(compatible)",
+				Found:    args[2].TypeName(),
+			}
+		}
+		return wrapError(fn(s1, i2, i3)), nil
+	}
+}
+
+// FuncAYRIE transform a function of 'func([]byte) (int, error)' signature
+// into CallableFunc type.
+func FuncAYRIE(fn func([]byte) (int, error)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		y1, ok := tengo.ToByteSlice(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "bytes(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		res, err := fn(y1)
+		if err != nil {
+			return wrapError(err), nil
+		}
+		return &tengo.Int{Value: int64(res)}, nil
+	}
+}
+
+// FuncAYRS transform a function of 'func([]byte) string' signature into
+// CallableFunc type.
+func FuncAYRS(fn func([]byte) string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		y1, ok := tengo.ToByteSlice(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "bytes(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		res := fn(y1)
+		return &tengo.String{Value: res}, nil
+	}
+}
+
+// FuncASRIE transform a function of 'func(string) (int, error)' signature
+// into CallableFunc type.
+func FuncASRIE(fn func(string) (int, error)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		res, err := fn(s1)
+		if err != nil {
+			return wrapError(err), nil
+		}
+		return &tengo.Int{Value: int64(res)}, nil
+	}
+}
+
+// FuncASRYE transform a function of 'func(string) ([]byte, error)' signature
+// into CallableFunc type.
+func FuncASRYE(fn func(string) ([]byte, error)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		s1, ok := tengo.ToString(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "string(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		res, err := fn(s1)
+		if err != nil {
+			return wrapError(err), nil
+		}
+		if len(res) > tengo.MaxBytesLen {
+			return nil, tengo.ErrBytesLimit
+		}
+		return &tengo.Bytes{Value: res}, nil
+	}
+}
+
+// FuncAIRSsE transform a function of 'func(int) ([]string, error)' signature
+// into CallableFunc type.
+func FuncAIRSsE(fn func(int) ([]string, error)) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		i1, ok := tengo.ToInt(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "int(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		res, err := fn(i1)
+		if err != nil {
+			return wrapError(err), nil
+		}
+		arr := &tengo.Array{}
+		for _, r := range res {
+			if len(r) > tengo.MaxStringLen {
+				return nil, tengo.ErrStringLimit
+			}
+			arr.Value = append(arr.Value, &tengo.String{Value: r})
+		}
+		return arr, nil
+	}
+}
+
+// FuncAIRS transform a function of 'func(int) string' signature into
+// CallableFunc type.
+func FuncAIRS(fn func(int) string) tengo.CallableFunc {
+	return func(args ...tengo.Object) (ret tengo.Object, err error) {
+		if len(args) != 1 {
+			return nil, tengo.ErrWrongNumArguments
+		}
+		i1, ok := tengo.ToInt(args[0])
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     "first",
+				Expected: "int(compatible)",
+				Found:    args[0].TypeName(),
+			}
+		}
+		s := fn(i1)
+		if len(s) > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		return &tengo.String{Value: s}, nil
+	}
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/hex.go b/vendor/github.com/d5/tengo/v2/stdlib/hex.go
new file mode 100644
index 00000000..981da696
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/hex.go
@@ -0,0 +1,12 @@
+package stdlib
+
+import (
+	"encoding/hex"
+
+	"github.com/d5/tengo/v2"
+)
+
+var hexModule = map[string]tengo.Object{
+	"encode": &tengo.UserFunction{Value: FuncAYRS(hex.EncodeToString)},
+	"decode": &tengo.UserFunction{Value: FuncASRYE(hex.DecodeString)},
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/json.go b/vendor/github.com/d5/tengo/v2/stdlib/json.go
new file mode 100644
index 00000000..be2185db
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/json.go
@@ -0,0 +1,146 @@
+package stdlib
+
+import (
+	"bytes"
+	gojson "encoding/json"
+
+	"github.com/d5/tengo/v2"
+	"github.com/d5/tengo/v2/stdlib/json"
+)
+
+var jsonModule = map[string]tengo.Object{
+	"decode": &tengo.UserFunction{
+		Name:  "decode",
+		Value: jsonDecode,
+	},
+	"encode": &tengo.UserFunction{
+		Name:  "encode",
+		Value: jsonEncode,
+	},
+	"indent": &tengo.UserFunction{
+		Name:  "encode",
+		Value: jsonIndent,
+	},
+	"html_escape": &tengo.UserFunction{
+		Name:  "html_escape",
+		Value: jsonHTMLEscape,
+	},
+}
+
+func jsonDecode(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+
+	switch o := args[0].(type) {
+	case *tengo.Bytes:
+		v, err := json.Decode(o.Value)
+		if err != nil {
+			return &tengo.Error{
+				Value: &tengo.String{Value: err.Error()},
+			}, nil
+		}
+		return v, nil
+	case *tengo.String:
+		v, err := json.Decode([]byte(o.Value))
+		if err != nil {
+			return &tengo.Error{
+				Value: &tengo.String{Value: err.Error()},
+			}, nil
+		}
+		return v, nil
+	default:
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "bytes/string",
+			Found:    args[0].TypeName(),
+		}
+	}
+}
+
+func jsonEncode(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+
+	b, err := json.Encode(args[0])
+	if err != nil {
+		return &tengo.Error{Value: &tengo.String{Value: err.Error()}}, nil
+	}
+
+	return &tengo.Bytes{Value: b}, nil
+}
+
+func jsonIndent(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 3 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+
+	prefix, ok := tengo.ToString(args[1])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "prefix",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+	}
+
+	indent, ok := tengo.ToString(args[2])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "indent",
+			Expected: "string(compatible)",
+			Found:    args[2].TypeName(),
+		}
+	}
+
+	switch o := args[0].(type) {
+	case *tengo.Bytes:
+		var dst bytes.Buffer
+		err := gojson.Indent(&dst, o.Value, prefix, indent)
+		if err != nil {
+			return &tengo.Error{
+				Value: &tengo.String{Value: err.Error()},
+			}, nil
+		}
+		return &tengo.Bytes{Value: dst.Bytes()}, nil
+	case *tengo.String:
+		var dst bytes.Buffer
+		err := gojson.Indent(&dst, []byte(o.Value), prefix, indent)
+		if err != nil {
+			return &tengo.Error{
+				Value: &tengo.String{Value: err.Error()},
+			}, nil
+		}
+		return &tengo.Bytes{Value: dst.Bytes()}, nil
+	default:
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "bytes/string",
+			Found:    args[0].TypeName(),
+		}
+	}
+}
+
+func jsonHTMLEscape(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+
+	switch o := args[0].(type) {
+	case *tengo.Bytes:
+		var dst bytes.Buffer
+		gojson.HTMLEscape(&dst, o.Value)
+		return &tengo.Bytes{Value: dst.Bytes()}, nil
+	case *tengo.String:
+		var dst bytes.Buffer
+		gojson.HTMLEscape(&dst, []byte(o.Value))
+		return &tengo.Bytes{Value: dst.Bytes()}, nil
+	default:
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "bytes/string",
+			Found:    args[0].TypeName(),
+		}
+	}
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/json/decode.go b/vendor/github.com/d5/tengo/v2/stdlib/json/decode.go
new file mode 100644
index 00000000..6d468ef0
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/json/decode.go
@@ -0,0 +1,358 @@
+// A modified version of Go's JSON implementation.
+
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package json
+
+import (
+	"strconv"
+	"unicode"
+	"unicode/utf16"
+	"unicode/utf8"
+
+	"github.com/d5/tengo/v2"
+)
+
+// Decode parses the JSON-encoded data and returns the result object.
+func Decode(data []byte) (tengo.Object, error) {
+	var d decodeState
+	err := checkValid(data, &d.scan)
+	if err != nil {
+		return nil, err
+	}
+	d.init(data)
+	d.scan.reset()
+	d.scanWhile(scanSkipSpace)
+	return d.value()
+}
+
+// decodeState represents the state while decoding a JSON value.
+type decodeState struct {
+	data   []byte
+	off    int // next read offset in data
+	opcode int // last read result
+	scan   scanner
+}
+
+// readIndex returns the position of the last byte read.
+func (d *decodeState) readIndex() int {
+	return d.off - 1
+}
+
+const phasePanicMsg = "JSON decoder out of sync - data changing underfoot?"
+
+func (d *decodeState) init(data []byte) *decodeState {
+	d.data = data
+	d.off = 0
+	return d
+}
+
+// scanNext processes the byte at d.data[d.off].
+func (d *decodeState) scanNext() {
+	if d.off < len(d.data) {
+		d.opcode = d.scan.step(&d.scan, d.data[d.off])
+		d.off++
+	} else {
+		d.opcode = d.scan.eof()
+		d.off = len(d.data) + 1 // mark processed EOF with len+1
+	}
+}
+
+// scanWhile processes bytes in d.data[d.off:] until it
+// receives a scan code not equal to op.
+func (d *decodeState) scanWhile(op int) {
+	s, data, i := &d.scan, d.data, d.off
+	for i < len(data) {
+		newOp := s.step(s, data[i])
+		i++
+		if newOp != op {
+			d.opcode = newOp
+			d.off = i
+			return
+		}
+	}
+
+	d.off = len(data) + 1 // mark processed EOF with len+1
+	d.opcode = d.scan.eof()
+}
+
+func (d *decodeState) value() (tengo.Object, error) {
+	switch d.opcode {
+	default:
+		panic(phasePanicMsg)
+	case scanBeginArray:
+		o, err := d.array()
+		if err != nil {
+			return nil, err
+		}
+		d.scanNext()
+		return o, nil
+	case scanBeginObject:
+		o, err := d.object()
+		if err != nil {
+			return nil, err
+		}
+		d.scanNext()
+		return o, nil
+	case scanBeginLiteral:
+		return d.literal()
+	}
+}
+
+func (d *decodeState) array() (tengo.Object, error) {
+	var arr []tengo.Object
+	for {
+		// Look ahead for ] - can only happen on first iteration.
+		d.scanWhile(scanSkipSpace)
+		if d.opcode == scanEndArray {
+			break
+		}
+		o, err := d.value()
+		if err != nil {
+			return nil, err
+		}
+		arr = append(arr, o)
+
+		// Next token must be , or ].
+		if d.opcode == scanSkipSpace {
+			d.scanWhile(scanSkipSpace)
+		}
+		if d.opcode == scanEndArray {
+			break
+		}
+		if d.opcode != scanArrayValue {
+			panic(phasePanicMsg)
+		}
+	}
+	return &tengo.Array{Value: arr}, nil
+}
+
+func (d *decodeState) object() (tengo.Object, error) {
+	m := make(map[string]tengo.Object)
+	for {
+		// Read opening " of string key or closing }.
+		d.scanWhile(scanSkipSpace)
+		if d.opcode == scanEndObject {
+			// closing } - can only happen on first iteration.
+			break
+		}
+		if d.opcode != scanBeginLiteral {
+			panic(phasePanicMsg)
+		}
+
+		// Read string key.
+		start := d.readIndex()
+		d.scanWhile(scanContinue)
+		item := d.data[start:d.readIndex()]
+		key, ok := unquote(item)
+		if !ok {
+			panic(phasePanicMsg)
+		}
+
+		// Read : before value.
+		if d.opcode == scanSkipSpace {
+			d.scanWhile(scanSkipSpace)
+		}
+		if d.opcode != scanObjectKey {
+			panic(phasePanicMsg)
+		}
+		d.scanWhile(scanSkipSpace)
+
+		// Read value.
+		o, err := d.value()
+		if err != nil {
+			return nil, err
+		}
+
+		m[key] = o
+
+		// Next token must be , or }.
+		if d.opcode == scanSkipSpace {
+			d.scanWhile(scanSkipSpace)
+		}
+		if d.opcode == scanEndObject {
+			break
+		}
+		if d.opcode != scanObjectValue {
+			panic(phasePanicMsg)
+		}
+	}
+	return &tengo.Map{Value: m}, nil
+}
+
+func (d *decodeState) literal() (tengo.Object, error) {
+	// All bytes inside literal return scanContinue op code.
+	start := d.readIndex()
+	d.scanWhile(scanContinue)
+
+	item := d.data[start:d.readIndex()]
+
+	switch c := item[0]; c {
+	case 'n': // null
+		return tengo.UndefinedValue, nil
+
+	case 't', 'f': // true, false
+		if c == 't' {
+			return tengo.TrueValue, nil
+		}
+		return tengo.FalseValue, nil
+
+	case '"': // string
+		s, ok := unquote(item)
+		if !ok {
+			panic(phasePanicMsg)
+		}
+		return &tengo.String{Value: s}, nil
+
+	default: // number
+		if c != '-' && (c < '0' || c > '9') {
+			panic(phasePanicMsg)
+		}
+		n, _ := strconv.ParseFloat(string(item), 10)
+		return &tengo.Float{Value: n}, nil
+	}
+}
+
+// getu4 decodes \uXXXX from the beginning of s, returning the hex value,
+// or it returns -1.
+func getu4(s []byte) rune {
+	if len(s) < 6 || s[0] != '\\' || s[1] != 'u' {
+		return -1
+	}
+	var r rune
+	for _, c := range s[2:6] {
+		switch {
+		case '0' <= c && c <= '9':
+			c = c - '0'
+		case 'a' <= c && c <= 'f':
+			c = c - 'a' + 10
+		case 'A' <= c && c <= 'F':
+			c = c - 'A' + 10
+		default:
+			return -1
+		}
+		r = r*16 + rune(c)
+	}
+	return r
+}
+
+// unquote converts a quoted JSON string literal s into an actual string t.
+// The rules are different than for Go, so cannot use strconv.Unquote.
+func unquote(s []byte) (t string, ok bool) {
+	s, ok = unquoteBytes(s)
+	t = string(s)
+	return
+}
+
+func unquoteBytes(s []byte) (t []byte, ok bool) {
+	if len(s) < 2 || s[0] != '"' || s[len(s)-1] != '"' {
+		return
+	}
+	s = s[1 : len(s)-1]
+
+	// Check for unusual characters. If there are none, then no unquoting is
+	// needed, so return a slice of the original bytes.
+	r := 0
+	for r < len(s) {
+		c := s[r]
+		if c == '\\' || c == '"' || c < ' ' {
+			break
+		}
+		if c < utf8.RuneSelf {
+			r++
+			continue
+		}
+		rr, size := utf8.DecodeRune(s[r:])
+		if rr == utf8.RuneError && size == 1 {
+			break
+		}
+		r += size
+	}
+	if r == len(s) {
+		return s, true
+	}
+
+	b := make([]byte, len(s)+2*utf8.UTFMax)
+	w := copy(b, s[0:r])
+	for r < len(s) {
+		// Out of room? Can only happen if s is full of
+		// malformed UTF-8 and we're replacing each
+		// byte with RuneError.
+		if w >= len(b)-2*utf8.UTFMax {
+			nb := make([]byte, (len(b)+utf8.UTFMax)*2)
+			copy(nb, b[0:w])
+			b = nb
+		}
+		switch c := s[r]; {
+		case c == '\\':
+			r++
+			if r >= len(s) {
+				return
+			}
+			switch s[r] {
+			default:
+				return
+			case '"', '\\', '/', '\'':
+				b[w] = s[r]
+				r++
+				w++
+			case 'b':
+				b[w] = '\b'
+				r++
+				w++
+			case 'f':
+				b[w] = '\f'
+				r++
+				w++
+			case 'n':
+				b[w] = '\n'
+				r++
+				w++
+			case 'r':
+				b[w] = '\r'
+				r++
+				w++
+			case 't':
+				b[w] = '\t'
+				r++
+				w++
+			case 'u':
+				r--
+				rr := getu4(s[r:])
+				if rr < 0 {
+					return
+				}
+				r += 6
+				if utf16.IsSurrogate(rr) {
+					rr1 := getu4(s[r:])
+					dec := utf16.DecodeRune(rr, rr1)
+					if dec != unicode.ReplacementChar {
+						// A valid pair; consume.
+						r += 6
+						w += utf8.EncodeRune(b[w:], dec)
+						break
+					}
+					// Invalid surrogate; fall back to replacement rune.
+					rr = unicode.ReplacementChar
+				}
+				w += utf8.EncodeRune(b[w:], rr)
+			}
+		// Quote, control characters are invalid.
+		case c == '"', c < ' ':
+			return
+		// ASCII
+		case c < utf8.RuneSelf:
+			b[w] = c
+			r++
+			w++
+		// Coerce to well-formed UTF-8.
+		default:
+			rr, size := utf8.DecodeRune(s[r:])
+			r += size
+			w += utf8.EncodeRune(b[w:], rr)
+		}
+	}
+	return b[0:w], true
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/json/encode.go b/vendor/github.com/d5/tengo/v2/stdlib/json/encode.go
new file mode 100644
index 00000000..ab7ca6ff
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/json/encode.go
@@ -0,0 +1,146 @@
+// A modified version of Go's JSON implementation.
+
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package json
+
+import (
+	"encoding/base64"
+	"errors"
+	"math"
+	"strconv"
+
+	"github.com/d5/tengo/v2"
+)
+
+// Encode returns the JSON encoding of the object.
+func Encode(o tengo.Object) ([]byte, error) {
+	var b []byte
+
+	switch o := o.(type) {
+	case *tengo.Array:
+		b = append(b, '[')
+		len1 := len(o.Value) - 1
+		for idx, elem := range o.Value {
+			eb, err := Encode(elem)
+			if err != nil {
+				return nil, err
+			}
+			b = append(b, eb...)
+			if idx < len1 {
+				b = append(b, ',')
+			}
+		}
+		b = append(b, ']')
+	case *tengo.ImmutableArray:
+		b = append(b, '[')
+		len1 := len(o.Value) - 1
+		for idx, elem := range o.Value {
+			eb, err := Encode(elem)
+			if err != nil {
+				return nil, err
+			}
+			b = append(b, eb...)
+			if idx < len1 {
+				b = append(b, ',')
+			}
+		}
+		b = append(b, ']')
+	case *tengo.Map:
+		b = append(b, '{')
+		len1 := len(o.Value) - 1
+		idx := 0
+		for key, value := range o.Value {
+			b = strconv.AppendQuote(b, key)
+			b = append(b, ':')
+			eb, err := Encode(value)
+			if err != nil {
+				return nil, err
+			}
+			b = append(b, eb...)
+			if idx < len1 {
+				b = append(b, ',')
+			}
+			idx++
+		}
+		b = append(b, '}')
+	case *tengo.ImmutableMap:
+		b = append(b, '{')
+		len1 := len(o.Value) - 1
+		idx := 0
+		for key, value := range o.Value {
+			b = strconv.AppendQuote(b, key)
+			b = append(b, ':')
+			eb, err := Encode(value)
+			if err != nil {
+				return nil, err
+			}
+			b = append(b, eb...)
+			if idx < len1 {
+				b = append(b, ',')
+			}
+			idx++
+		}
+		b = append(b, '}')
+	case *tengo.Bool:
+		if o.IsFalsy() {
+			b = strconv.AppendBool(b, false)
+		} else {
+			b = strconv.AppendBool(b, true)
+		}
+	case *tengo.Bytes:
+		b = append(b, '"')
+		encodedLen := base64.StdEncoding.EncodedLen(len(o.Value))
+		dst := make([]byte, encodedLen)
+		base64.StdEncoding.Encode(dst, o.Value)
+		b = append(b, dst...)
+		b = append(b, '"')
+	case *tengo.Char:
+		b = strconv.AppendInt(b, int64(o.Value), 10)
+	case *tengo.Float:
+		var y []byte
+
+		f := o.Value
+		if math.IsInf(f, 0) || math.IsNaN(f) {
+			return nil, errors.New("unsupported float value")
+		}
+
+		// Convert as if by ES6 number to string conversion.
+		// This matches most other JSON generators.
+		abs := math.Abs(f)
+		fmt := byte('f')
+		if abs != 0 {
+			if abs < 1e-6 || abs >= 1e21 {
+				fmt = 'e'
+			}
+		}
+		y = strconv.AppendFloat(y, f, fmt, -1, 64)
+		if fmt == 'e' {
+			// clean up e-09 to e-9
+			n := len(y)
+			if n >= 4 && y[n-4] == 'e' && y[n-3] == '-' && y[n-2] == '0' {
+				y[n-2] = y[n-1]
+				y = y[:n-1]
+			}
+		}
+
+		b = append(b, y...)
+	case *tengo.Int:
+		b = strconv.AppendInt(b, o.Value, 10)
+	case *tengo.String:
+		b = strconv.AppendQuote(b, o.Value)
+	case *tengo.Time:
+		y, err := o.Value.MarshalJSON()
+		if err != nil {
+			return nil, err
+		}
+		b = append(b, y...)
+	case *tengo.Undefined:
+		b = append(b, "null"...)
+	default:
+		// unknown type: ignore
+	}
+	return b, nil
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/json/scanner.go b/vendor/github.com/d5/tengo/v2/stdlib/json/scanner.go
new file mode 100644
index 00000000..aed15cf5
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/json/scanner.go
@@ -0,0 +1,562 @@
+// A modified version of Go's JSON implementation.
+
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package json
+
+import "strconv"
+
+func checkValid(data []byte, scan *scanner) error {
+	scan.reset()
+	for _, c := range data {
+		scan.bytes++
+		if scan.step(scan, c) == scanError {
+			return scan.err
+		}
+	}
+	if scan.eof() == scanError {
+		return scan.err
+	}
+	return nil
+}
+
+// A SyntaxError is a description of a JSON syntax error.
+type SyntaxError struct {
+	msg    string // description of error
+	Offset int64  // error occurred after reading Offset bytes
+}
+
+func (e *SyntaxError) Error() string { return e.msg }
+
+// A scanner is a JSON scanning state machine.
+// Callers call scan.reset() and then pass bytes in one at a time
+// by calling scan.step(&scan, c) for each byte.
+// The return value, referred to as an opcode, tells the
+// caller about significant parsing events like beginning
+// and ending literals, objects, and arrays, so that the
+// caller can follow along if it wishes.
+// The return value scanEnd indicates that a single top-level
+// JSON value has been completed, *before* the byte that
+// just got passed in.  (The indication must be delayed in order
+// to recognize the end of numbers: is 123 a whole value or
+// the beginning of 12345e+6?).
+type scanner struct {
+	// The step is a func to be called to execute the next transition.
+	// Also tried using an integer constant and a single func
+	// with a switch, but using the func directly was 10% faster
+	// on a 64-bit Mac Mini, and it's nicer to read.
+	step func(*scanner, byte) int
+
+	// Reached end of top-level value.
+	endTop bool
+
+	// Stack of what we're in the middle of - array values, object keys, object values.
+	parseState []int
+
+	// Error that happened, if any.
+	err error
+
+	// total bytes consumed, updated by decoder.Decode
+	bytes int64
+}
+
+// These values are returned by the state transition functions
+// assigned to scanner.state and the method scanner.eof.
+// They give details about the current state of the scan that
+// callers might be interested to know about.
+// It is okay to ignore the return value of any particular
+// call to scanner.state: if one call returns scanError,
+// every subsequent call will return scanError too.
+const (
+	// Continue.
+	scanContinue     = iota // uninteresting byte
+	scanBeginLiteral        // end implied by next result != scanContinue
+	scanBeginObject         // begin object
+	scanObjectKey           // just finished object key (string)
+	scanObjectValue         // just finished non-last object value
+	scanEndObject           // end object (implies scanObjectValue if possible)
+	scanBeginArray          // begin array
+	scanArrayValue          // just finished array value
+	scanEndArray            // end array (implies scanArrayValue if possible)
+	scanSkipSpace           // space byte; can skip; known to be last "continue" result
+
+	// Stop.
+	scanEnd   // top-level value ended *before* this byte; known to be first "stop" result
+	scanError // hit an error, scanner.err.
+)
+
+// These values are stored in the parseState stack.
+// They give the current state of a composite value
+// being scanned. If the parser is inside a nested value
+// the parseState describes the nested state, outermost at entry 0.
+const (
+	parseObjectKey   = iota // parsing object key (before colon)
+	parseObjectValue        // parsing object value (after colon)
+	parseArrayValue         // parsing array value
+)
+
+// reset prepares the scanner for use.
+// It must be called before calling s.step.
+func (s *scanner) reset() {
+	s.step = stateBeginValue
+	s.parseState = s.parseState[0:0]
+	s.err = nil
+	s.endTop = false
+}
+
+// eof tells the scanner that the end of input has been reached.
+// It returns a scan status just as s.step does.
+func (s *scanner) eof() int {
+	if s.err != nil {
+		return scanError
+	}
+	if s.endTop {
+		return scanEnd
+	}
+	s.step(s, ' ')
+	if s.endTop {
+		return scanEnd
+	}
+	if s.err == nil {
+		s.err = &SyntaxError{"unexpected end of JSON input", s.bytes}
+	}
+	return scanError
+}
+
+// pushParseState pushes a new parse state p onto the parse stack.
+func (s *scanner) pushParseState(p int) {
+	s.parseState = append(s.parseState, p)
+}
+
+// popParseState pops a parse state (already obtained) off the stack
+// and updates s.step accordingly.
+func (s *scanner) popParseState() {
+	n := len(s.parseState) - 1
+	s.parseState = s.parseState[0:n]
+	if n == 0 {
+		s.step = stateEndTop
+		s.endTop = true
+	} else {
+		s.step = stateEndValue
+	}
+}
+
+func isSpace(c byte) bool {
+	return c == ' ' || c == '\t' || c == '\r' || c == '\n'
+}
+
+// stateBeginValueOrEmpty is the state after reading `[`.
+func stateBeginValueOrEmpty(s *scanner, c byte) int {
+	if c <= ' ' && isSpace(c) {
+		return scanSkipSpace
+	}
+	if c == ']' {
+		return stateEndValue(s, c)
+	}
+	return stateBeginValue(s, c)
+}
+
+// stateBeginValue is the state at the beginning of the input.
+func stateBeginValue(s *scanner, c byte) int {
+	if c <= ' ' && isSpace(c) {
+		return scanSkipSpace
+	}
+	switch c {
+	case '{':
+		s.step = stateBeginStringOrEmpty
+		s.pushParseState(parseObjectKey)
+		return scanBeginObject
+	case '[':
+		s.step = stateBeginValueOrEmpty
+		s.pushParseState(parseArrayValue)
+		return scanBeginArray
+	case '"':
+		s.step = stateInString
+		return scanBeginLiteral
+	case '-':
+		s.step = stateNeg
+		return scanBeginLiteral
+	case '0': // beginning of 0.123
+		s.step = state0
+		return scanBeginLiteral
+	case 't': // beginning of true
+		s.step = stateT
+		return scanBeginLiteral
+	case 'f': // beginning of false
+		s.step = stateF
+		return scanBeginLiteral
+	case 'n': // beginning of null
+		s.step = stateN
+		return scanBeginLiteral
+	}
+	if '1' <= c && c <= '9' { // beginning of 1234.5
+		s.step = state1
+		return scanBeginLiteral
+	}
+	return s.error(c, "looking for beginning of value")
+}
+
+// stateBeginStringOrEmpty is the state after reading `{`.
+func stateBeginStringOrEmpty(s *scanner, c byte) int {
+	if c <= ' ' && isSpace(c) {
+		return scanSkipSpace
+	}
+	if c == '}' {
+		n := len(s.parseState)
+		s.parseState[n-1] = parseObjectValue
+		return stateEndValue(s, c)
+	}
+	return stateBeginString(s, c)
+}
+
+// stateBeginString is the state after reading `{"key": value,`.
+func stateBeginString(s *scanner, c byte) int {
+	if c <= ' ' && isSpace(c) {
+		return scanSkipSpace
+	}
+	if c == '"' {
+		s.step = stateInString
+		return scanBeginLiteral
+	}
+	return s.error(c, "looking for beginning of object key string")
+}
+
+// stateEndValue is the state after completing a value,
+// such as after reading `{}` or `true` or `["x"`.
+func stateEndValue(s *scanner, c byte) int {
+	n := len(s.parseState)
+	if n == 0 {
+		// Completed top-level before the current byte.
+		s.step = stateEndTop
+		s.endTop = true
+		return stateEndTop(s, c)
+	}
+	if c <= ' ' && isSpace(c) {
+		s.step = stateEndValue
+		return scanSkipSpace
+	}
+	ps := s.parseState[n-1]
+	switch ps {
+	case parseObjectKey:
+		if c == ':' {
+			s.parseState[n-1] = parseObjectValue
+			s.step = stateBeginValue
+			return scanObjectKey
+		}
+		return s.error(c, "after object key")
+	case parseObjectValue:
+		if c == ',' {
+			s.parseState[n-1] = parseObjectKey
+			s.step = stateBeginString
+			return scanObjectValue
+		}
+		if c == '}' {
+			s.popParseState()
+			return scanEndObject
+		}
+		return s.error(c, "after object key:value pair")
+	case parseArrayValue:
+		if c == ',' {
+			s.step = stateBeginValue
+			return scanArrayValue
+		}
+		if c == ']' {
+			s.popParseState()
+			return scanEndArray
+		}
+		return s.error(c, "after array element")
+	}
+	return s.error(c, "")
+}
+
+// stateEndTop is the state after finishing the top-level value,
+// such as after reading `{}` or `[1,2,3]`.
+// Only space characters should be seen now.
+func stateEndTop(s *scanner, c byte) int {
+	if !isSpace(c) {
+		// Complain about non-space byte on next call.
+		s.error(c, "after top-level value")
+	}
+	return scanEnd
+}
+
+// stateInString is the state after reading `"`.
+func stateInString(s *scanner, c byte) int {
+	if c == '"' {
+		s.step = stateEndValue
+		return scanContinue
+	}
+	if c == '\\' {
+		s.step = stateInStringEsc
+		return scanContinue
+	}
+	if c < 0x20 {
+		return s.error(c, "in string literal")
+	}
+	return scanContinue
+}
+
+// stateInStringEsc is the state after reading `"\` during a quoted string.
+func stateInStringEsc(s *scanner, c byte) int {
+	switch c {
+	case 'b', 'f', 'n', 'r', 't', '\\', '/', '"':
+		s.step = stateInString
+		return scanContinue
+	case 'u':
+		s.step = stateInStringEscU
+		return scanContinue
+	}
+	return s.error(c, "in string escape code")
+}
+
+// stateInStringEscU is the state after reading `"\u` during a quoted string.
+func stateInStringEscU(s *scanner, c byte) int {
+	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
+		s.step = stateInStringEscU1
+		return scanContinue
+	}
+	// numbers
+	return s.error(c, "in \\u hexadecimal character escape")
+}
+
+// stateInStringEscU1 is the state after reading `"\u1` during a quoted string.
+func stateInStringEscU1(s *scanner, c byte) int {
+	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
+		s.step = stateInStringEscU12
+		return scanContinue
+	}
+	// numbers
+	return s.error(c, "in \\u hexadecimal character escape")
+}
+
+// stateInStringEscU12 is the state after reading `"\u12` during a quoted string.
+func stateInStringEscU12(s *scanner, c byte) int {
+	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
+		s.step = stateInStringEscU123
+		return scanContinue
+	}
+	// numbers
+	return s.error(c, "in \\u hexadecimal character escape")
+}
+
+// stateInStringEscU123 is the state after reading `"\u123` during a quoted string.
+func stateInStringEscU123(s *scanner, c byte) int {
+	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
+		s.step = stateInString
+		return scanContinue
+	}
+	// numbers
+	return s.error(c, "in \\u hexadecimal character escape")
+}
+
+// stateNeg is the state after reading `-` during a number.
+func stateNeg(s *scanner, c byte) int {
+	if c == '0' {
+		s.step = state0
+		return scanContinue
+	}
+	if '1' <= c && c <= '9' {
+		s.step = state1
+		return scanContinue
+	}
+	return s.error(c, "in numeric literal")
+}
+
+// state1 is the state after reading a non-zero integer during a number,
+// such as after reading `1` or `100` but not `0`.
+func state1(s *scanner, c byte) int {
+	if '0' <= c && c <= '9' {
+		s.step = state1
+		return scanContinue
+	}
+	return state0(s, c)
+}
+
+// state0 is the state after reading `0` during a number.
+func state0(s *scanner, c byte) int {
+	if c == '.' {
+		s.step = stateDot
+		return scanContinue
+	}
+	if c == 'e' || c == 'E' {
+		s.step = stateE
+		return scanContinue
+	}
+	return stateEndValue(s, c)
+}
+
+// stateDot is the state after reading the integer and decimal point in a number,
+// such as after reading `1.`.
+func stateDot(s *scanner, c byte) int {
+	if '0' <= c && c <= '9' {
+		s.step = stateDot0
+		return scanContinue
+	}
+	return s.error(c, "after decimal point in numeric literal")
+}
+
+// stateDot0 is the state after reading the integer, decimal point, and subsequent
+// digits of a number, such as after reading `3.14`.
+func stateDot0(s *scanner, c byte) int {
+	if '0' <= c && c <= '9' {
+		return scanContinue
+	}
+	if c == 'e' || c == 'E' {
+		s.step = stateE
+		return scanContinue
+	}
+	return stateEndValue(s, c)
+}
+
+// stateE is the state after reading the mantissa and e in a number,
+// such as after reading `314e` or `0.314e`.
+func stateE(s *scanner, c byte) int {
+	if c == '+' || c == '-' {
+		s.step = stateESign
+		return scanContinue
+	}
+	return stateESign(s, c)
+}
+
+// stateESign is the state after reading the mantissa, e, and sign in a number,
+// such as after reading `314e-` or `0.314e+`.
+func stateESign(s *scanner, c byte) int {
+	if '0' <= c && c <= '9' {
+		s.step = stateE0
+		return scanContinue
+	}
+	return s.error(c, "in exponent of numeric literal")
+}
+
+// stateE0 is the state after reading the mantissa, e, optional sign,
+// and at least one digit of the exponent in a number,
+// such as after reading `314e-2` or `0.314e+1` or `3.14e0`.
+func stateE0(s *scanner, c byte) int {
+	if '0' <= c && c <= '9' {
+		return scanContinue
+	}
+	return stateEndValue(s, c)
+}
+
+// stateT is the state after reading `t`.
+func stateT(s *scanner, c byte) int {
+	if c == 'r' {
+		s.step = stateTr
+		return scanContinue
+	}
+	return s.error(c, "in literal true (expecting 'r')")
+}
+
+// stateTr is the state after reading `tr`.
+func stateTr(s *scanner, c byte) int {
+	if c == 'u' {
+		s.step = stateTru
+		return scanContinue
+	}
+	return s.error(c, "in literal true (expecting 'u')")
+}
+
+// stateTru is the state after reading `tru`.
+func stateTru(s *scanner, c byte) int {
+	if c == 'e' {
+		s.step = stateEndValue
+		return scanContinue
+	}
+	return s.error(c, "in literal true (expecting 'e')")
+}
+
+// stateF is the state after reading `f`.
+func stateF(s *scanner, c byte) int {
+	if c == 'a' {
+		s.step = stateFa
+		return scanContinue
+	}
+	return s.error(c, "in literal false (expecting 'a')")
+}
+
+// stateFa is the state after reading `fa`.
+func stateFa(s *scanner, c byte) int {
+	if c == 'l' {
+		s.step = stateFal
+		return scanContinue
+	}
+	return s.error(c, "in literal false (expecting 'l')")
+}
+
+// stateFal is the state after reading `fal`.
+func stateFal(s *scanner, c byte) int {
+	if c == 's' {
+		s.step = stateFals
+		return scanContinue
+	}
+	return s.error(c, "in literal false (expecting 's')")
+}
+
+// stateFals is the state after reading `fals`.
+func stateFals(s *scanner, c byte) int {
+	if c == 'e' {
+		s.step = stateEndValue
+		return scanContinue
+	}
+	return s.error(c, "in literal false (expecting 'e')")
+}
+
+// stateN is the state after reading `n`.
+func stateN(s *scanner, c byte) int {
+	if c == 'u' {
+		s.step = stateNu
+		return scanContinue
+	}
+	return s.error(c, "in literal null (expecting 'u')")
+}
+
+// stateNu is the state after reading `nu`.
+func stateNu(s *scanner, c byte) int {
+	if c == 'l' {
+		s.step = stateNul
+		return scanContinue
+	}
+	return s.error(c, "in literal null (expecting 'l')")
+}
+
+// stateNul is the state after reading `nul`.
+func stateNul(s *scanner, c byte) int {
+	if c == 'l' {
+		s.step = stateEndValue
+		return scanContinue
+	}
+	return s.error(c, "in literal null (expecting 'l')")
+}
+
+// stateError is the state after reaching a syntax error,
+// such as after reading `[1}` or `5.1.2`.
+func stateError(_ *scanner, _ byte) int {
+	return scanError
+}
+
+// error records an error and switches to the error state.
+func (s *scanner) error(c byte, context string) int {
+	s.step = stateError
+	s.err = &SyntaxError{
+		msg:    "invalid character " + quoteChar(c) + " " + context,
+		Offset: s.bytes,
+	}
+	return scanError
+}
+
+// quoteChar formats c as a quoted character literal
+func quoteChar(c byte) string {
+	// special cases - different from quoted strings
+	if c == '\'' {
+		return `'\''`
+	}
+	if c == '"' {
+		return `'"'`
+	}
+
+	// use quoted string with different quotation marks
+	s := strconv.Quote(string(c))
+	return "'" + s[1:len(s)-1] + "'"
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/math.go b/vendor/github.com/d5/tengo/v2/stdlib/math.go
new file mode 100644
index 00000000..633ea09f
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/math.go
@@ -0,0 +1,233 @@
+package stdlib
+
+import (
+	"math"
+
+	"github.com/d5/tengo/v2"
+)
+
+var mathModule = map[string]tengo.Object{
+	"e":       &tengo.Float{Value: math.E},
+	"pi":      &tengo.Float{Value: math.Pi},
+	"phi":     &tengo.Float{Value: math.Phi},
+	"sqrt2":   &tengo.Float{Value: math.Sqrt2},
+	"sqrtE":   &tengo.Float{Value: math.SqrtE},
+	"sqrtPi":  &tengo.Float{Value: math.SqrtPi},
+	"sqrtPhi": &tengo.Float{Value: math.SqrtPhi},
+	"ln2":     &tengo.Float{Value: math.Ln2},
+	"log2E":   &tengo.Float{Value: math.Log2E},
+	"ln10":    &tengo.Float{Value: math.Ln10},
+	"log10E":  &tengo.Float{Value: math.Log10E},
+	"abs": &tengo.UserFunction{
+		Name:  "abs",
+		Value: FuncAFRF(math.Abs),
+	},
+	"acos": &tengo.UserFunction{
+		Name:  "acos",
+		Value: FuncAFRF(math.Acos),
+	},
+	"acosh": &tengo.UserFunction{
+		Name:  "acosh",
+		Value: FuncAFRF(math.Acosh),
+	},
+	"asin": &tengo.UserFunction{
+		Name:  "asin",
+		Value: FuncAFRF(math.Asin),
+	},
+	"asinh": &tengo.UserFunction{
+		Name:  "asinh",
+		Value: FuncAFRF(math.Asinh),
+	},
+	"atan": &tengo.UserFunction{
+		Name:  "atan",
+		Value: FuncAFRF(math.Atan),
+	},
+	"atan2": &tengo.UserFunction{
+		Name:  "atan2",
+		Value: FuncAFFRF(math.Atan2),
+	},
+	"atanh": &tengo.UserFunction{
+		Name:  "atanh",
+		Value: FuncAFRF(math.Atanh),
+	},
+	"cbrt": &tengo.UserFunction{
+		Name:  "cbrt",
+		Value: FuncAFRF(math.Cbrt),
+	},
+	"ceil": &tengo.UserFunction{
+		Name:  "ceil",
+		Value: FuncAFRF(math.Ceil),
+	},
+	"copysign": &tengo.UserFunction{
+		Name:  "copysign",
+		Value: FuncAFFRF(math.Copysign),
+	},
+	"cos": &tengo.UserFunction{
+		Name:  "cos",
+		Value: FuncAFRF(math.Cos),
+	},
+	"cosh": &tengo.UserFunction{
+		Name:  "cosh",
+		Value: FuncAFRF(math.Cosh),
+	},
+	"dim": &tengo.UserFunction{
+		Name:  "dim",
+		Value: FuncAFFRF(math.Dim),
+	},
+	"erf": &tengo.UserFunction{
+		Name:  "erf",
+		Value: FuncAFRF(math.Erf),
+	},
+	"erfc": &tengo.UserFunction{
+		Name:  "erfc",
+		Value: FuncAFRF(math.Erfc),
+	},
+	"exp": &tengo.UserFunction{
+		Name:  "exp",
+		Value: FuncAFRF(math.Exp),
+	},
+	"exp2": &tengo.UserFunction{
+		Name:  "exp2",
+		Value: FuncAFRF(math.Exp2),
+	},
+	"expm1": &tengo.UserFunction{
+		Name:  "expm1",
+		Value: FuncAFRF(math.Expm1),
+	},
+	"floor": &tengo.UserFunction{
+		Name:  "floor",
+		Value: FuncAFRF(math.Floor),
+	},
+	"gamma": &tengo.UserFunction{
+		Name:  "gamma",
+		Value: FuncAFRF(math.Gamma),
+	},
+	"hypot": &tengo.UserFunction{
+		Name:  "hypot",
+		Value: FuncAFFRF(math.Hypot),
+	},
+	"ilogb": &tengo.UserFunction{
+		Name:  "ilogb",
+		Value: FuncAFRI(math.Ilogb),
+	},
+	"inf": &tengo.UserFunction{
+		Name:  "inf",
+		Value: FuncAIRF(math.Inf),
+	},
+	"is_inf": &tengo.UserFunction{
+		Name:  "is_inf",
+		Value: FuncAFIRB(math.IsInf),
+	},
+	"is_nan": &tengo.UserFunction{
+		Name:  "is_nan",
+		Value: FuncAFRB(math.IsNaN),
+	},
+	"j0": &tengo.UserFunction{
+		Name:  "j0",
+		Value: FuncAFRF(math.J0),
+	},
+	"j1": &tengo.UserFunction{
+		Name:  "j1",
+		Value: FuncAFRF(math.J1),
+	},
+	"jn": &tengo.UserFunction{
+		Name:  "jn",
+		Value: FuncAIFRF(math.Jn),
+	},
+	"ldexp": &tengo.UserFunction{
+		Name:  "ldexp",
+		Value: FuncAFIRF(math.Ldexp),
+	},
+	"log": &tengo.UserFunction{
+		Name:  "log",
+		Value: FuncAFRF(math.Log),
+	},
+	"log10": &tengo.UserFunction{
+		Name:  "log10",
+		Value: FuncAFRF(math.Log10),
+	},
+	"log1p": &tengo.UserFunction{
+		Name:  "log1p",
+		Value: FuncAFRF(math.Log1p),
+	},
+	"log2": &tengo.UserFunction{
+		Name:  "log2",
+		Value: FuncAFRF(math.Log2),
+	},
+	"logb": &tengo.UserFunction{
+		Name:  "logb",
+		Value: FuncAFRF(math.Logb),
+	},
+	"max": &tengo.UserFunction{
+		Name:  "max",
+		Value: FuncAFFRF(math.Max),
+	},
+	"min": &tengo.UserFunction{
+		Name:  "min",
+		Value: FuncAFFRF(math.Min),
+	},
+	"mod": &tengo.UserFunction{
+		Name:  "mod",
+		Value: FuncAFFRF(math.Mod),
+	},
+	"nan": &tengo.UserFunction{
+		Name:  "nan",
+		Value: FuncARF(math.NaN),
+	},
+	"nextafter": &tengo.UserFunction{
+		Name:  "nextafter",
+		Value: FuncAFFRF(math.Nextafter),
+	},
+	"pow": &tengo.UserFunction{
+		Name:  "pow",
+		Value: FuncAFFRF(math.Pow),
+	},
+	"pow10": &tengo.UserFunction{
+		Name:  "pow10",
+		Value: FuncAIRF(math.Pow10),
+	},
+	"remainder": &tengo.UserFunction{
+		Name:  "remainder",
+		Value: FuncAFFRF(math.Remainder),
+	},
+	"signbit": &tengo.UserFunction{
+		Name:  "signbit",
+		Value: FuncAFRB(math.Signbit),
+	},
+	"sin": &tengo.UserFunction{
+		Name:  "sin",
+		Value: FuncAFRF(math.Sin),
+	},
+	"sinh": &tengo.UserFunction{
+		Name:  "sinh",
+		Value: FuncAFRF(math.Sinh),
+	},
+	"sqrt": &tengo.UserFunction{
+		Name:  "sqrt",
+		Value: FuncAFRF(math.Sqrt),
+	},
+	"tan": &tengo.UserFunction{
+		Name:  "tan",
+		Value: FuncAFRF(math.Tan),
+	},
+	"tanh": &tengo.UserFunction{
+		Name:  "tanh",
+		Value: FuncAFRF(math.Tanh),
+	},
+	"trunc": &tengo.UserFunction{
+		Name:  "trunc",
+		Value: FuncAFRF(math.Trunc),
+	},
+	"y0": &tengo.UserFunction{
+		Name:  "y0",
+		Value: FuncAFRF(math.Y0),
+	},
+	"y1": &tengo.UserFunction{
+		Name:  "y1",
+		Value: FuncAFRF(math.Y1),
+	},
+	"yn": &tengo.UserFunction{
+		Name:  "yn",
+		Value: FuncAIFRF(math.Yn),
+	},
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/os.go b/vendor/github.com/d5/tengo/v2/stdlib/os.go
new file mode 100644
index 00000000..576bc94b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/os.go
@@ -0,0 +1,564 @@
+package stdlib
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+
+	"github.com/d5/tengo/v2"
+)
+
+var osModule = map[string]tengo.Object{
+	"o_rdonly":            &tengo.Int{Value: int64(os.O_RDONLY)},
+	"o_wronly":            &tengo.Int{Value: int64(os.O_WRONLY)},
+	"o_rdwr":              &tengo.Int{Value: int64(os.O_RDWR)},
+	"o_append":            &tengo.Int{Value: int64(os.O_APPEND)},
+	"o_create":            &tengo.Int{Value: int64(os.O_CREATE)},
+	"o_excl":              &tengo.Int{Value: int64(os.O_EXCL)},
+	"o_sync":              &tengo.Int{Value: int64(os.O_SYNC)},
+	"o_trunc":             &tengo.Int{Value: int64(os.O_TRUNC)},
+	"mode_dir":            &tengo.Int{Value: int64(os.ModeDir)},
+	"mode_append":         &tengo.Int{Value: int64(os.ModeAppend)},
+	"mode_exclusive":      &tengo.Int{Value: int64(os.ModeExclusive)},
+	"mode_temporary":      &tengo.Int{Value: int64(os.ModeTemporary)},
+	"mode_symlink":        &tengo.Int{Value: int64(os.ModeSymlink)},
+	"mode_device":         &tengo.Int{Value: int64(os.ModeDevice)},
+	"mode_named_pipe":     &tengo.Int{Value: int64(os.ModeNamedPipe)},
+	"mode_socket":         &tengo.Int{Value: int64(os.ModeSocket)},
+	"mode_setuid":         &tengo.Int{Value: int64(os.ModeSetuid)},
+	"mode_setgui":         &tengo.Int{Value: int64(os.ModeSetgid)},
+	"mode_char_device":    &tengo.Int{Value: int64(os.ModeCharDevice)},
+	"mode_sticky":         &tengo.Int{Value: int64(os.ModeSticky)},
+	"mode_type":           &tengo.Int{Value: int64(os.ModeType)},
+	"mode_perm":           &tengo.Int{Value: int64(os.ModePerm)},
+	"path_separator":      &tengo.Char{Value: os.PathSeparator},
+	"path_list_separator": &tengo.Char{Value: os.PathListSeparator},
+	"dev_null":            &tengo.String{Value: os.DevNull},
+	"seek_set":            &tengo.Int{Value: int64(io.SeekStart)},
+	"seek_cur":            &tengo.Int{Value: int64(io.SeekCurrent)},
+	"seek_end":            &tengo.Int{Value: int64(io.SeekEnd)},
+	"args": &tengo.UserFunction{
+		Name:  "args",
+		Value: osArgs,
+	}, // args() => array(string)
+	"chdir": &tengo.UserFunction{
+		Name:  "chdir",
+		Value: FuncASRE(os.Chdir),
+	}, // chdir(dir string) => error
+	"chmod": osFuncASFmRE("chmod", os.Chmod), // chmod(name string, mode int) => error
+	"chown": &tengo.UserFunction{
+		Name:  "chown",
+		Value: FuncASIIRE(os.Chown),
+	}, // chown(name string, uid int, gid int) => error
+	"clearenv": &tengo.UserFunction{
+		Name:  "clearenv",
+		Value: FuncAR(os.Clearenv),
+	}, // clearenv()
+	"environ": &tengo.UserFunction{
+		Name:  "environ",
+		Value: FuncARSs(os.Environ),
+	}, // environ() => array(string)
+	"exit": &tengo.UserFunction{
+		Name:  "exit",
+		Value: FuncAIR(os.Exit),
+	}, // exit(code int)
+	"expand_env": &tengo.UserFunction{
+		Name:  "expand_env",
+		Value: osExpandEnv,
+	}, // expand_env(s string) => string
+	"getegid": &tengo.UserFunction{
+		Name:  "getegid",
+		Value: FuncARI(os.Getegid),
+	}, // getegid() => int
+	"getenv": &tengo.UserFunction{
+		Name:  "getenv",
+		Value: FuncASRS(os.Getenv),
+	}, // getenv(s string) => string
+	"geteuid": &tengo.UserFunction{
+		Name:  "geteuid",
+		Value: FuncARI(os.Geteuid),
+	}, // geteuid() => int
+	"getgid": &tengo.UserFunction{
+		Name:  "getgid",
+		Value: FuncARI(os.Getgid),
+	}, // getgid() => int
+	"getgroups": &tengo.UserFunction{
+		Name:  "getgroups",
+		Value: FuncARIsE(os.Getgroups),
+	}, // getgroups() => array(string)/error
+	"getpagesize": &tengo.UserFunction{
+		Name:  "getpagesize",
+		Value: FuncARI(os.Getpagesize),
+	}, // getpagesize() => int
+	"getpid": &tengo.UserFunction{
+		Name:  "getpid",
+		Value: FuncARI(os.Getpid),
+	}, // getpid() => int
+	"getppid": &tengo.UserFunction{
+		Name:  "getppid",
+		Value: FuncARI(os.Getppid),
+	}, // getppid() => int
+	"getuid": &tengo.UserFunction{
+		Name:  "getuid",
+		Value: FuncARI(os.Getuid),
+	}, // getuid() => int
+	"getwd": &tengo.UserFunction{
+		Name:  "getwd",
+		Value: FuncARSE(os.Getwd),
+	}, // getwd() => string/error
+	"hostname": &tengo.UserFunction{
+		Name:  "hostname",
+		Value: FuncARSE(os.Hostname),
+	}, // hostname() => string/error
+	"lchown": &tengo.UserFunction{
+		Name:  "lchown",
+		Value: FuncASIIRE(os.Lchown),
+	}, // lchown(name string, uid int, gid int) => error
+	"link": &tengo.UserFunction{
+		Name:  "link",
+		Value: FuncASSRE(os.Link),
+	}, // link(oldname string, newname string) => error
+	"lookup_env": &tengo.UserFunction{
+		Name:  "lookup_env",
+		Value: osLookupEnv,
+	}, // lookup_env(key string) => string/false
+	"mkdir":     osFuncASFmRE("mkdir", os.Mkdir),        // mkdir(name string, perm int) => error
+	"mkdir_all": osFuncASFmRE("mkdir_all", os.MkdirAll), // mkdir_all(name string, perm int) => error
+	"readlink": &tengo.UserFunction{
+		Name:  "readlink",
+		Value: FuncASRSE(os.Readlink),
+	}, // readlink(name string) => string/error
+	"remove": &tengo.UserFunction{
+		Name:  "remove",
+		Value: FuncASRE(os.Remove),
+	}, // remove(name string) => error
+	"remove_all": &tengo.UserFunction{
+		Name:  "remove_all",
+		Value: FuncASRE(os.RemoveAll),
+	}, // remove_all(name string) => error
+	"rename": &tengo.UserFunction{
+		Name:  "rename",
+		Value: FuncASSRE(os.Rename),
+	}, // rename(oldpath string, newpath string) => error
+	"setenv": &tengo.UserFunction{
+		Name:  "setenv",
+		Value: FuncASSRE(os.Setenv),
+	}, // setenv(key string, value string) => error
+	"symlink": &tengo.UserFunction{
+		Name:  "symlink",
+		Value: FuncASSRE(os.Symlink),
+	}, // symlink(oldname string newname string) => error
+	"temp_dir": &tengo.UserFunction{
+		Name:  "temp_dir",
+		Value: FuncARS(os.TempDir),
+	}, // temp_dir() => string
+	"truncate": &tengo.UserFunction{
+		Name:  "truncate",
+		Value: FuncASI64RE(os.Truncate),
+	}, // truncate(name string, size int) => error
+	"unsetenv": &tengo.UserFunction{
+		Name:  "unsetenv",
+		Value: FuncASRE(os.Unsetenv),
+	}, // unsetenv(key string) => error
+	"create": &tengo.UserFunction{
+		Name:  "create",
+		Value: osCreate,
+	}, // create(name string) => imap(file)/error
+	"open": &tengo.UserFunction{
+		Name:  "open",
+		Value: osOpen,
+	}, // open(name string) => imap(file)/error
+	"open_file": &tengo.UserFunction{
+		Name:  "open_file",
+		Value: osOpenFile,
+	}, // open_file(name string, flag int, perm int) => imap(file)/error
+	"find_process": &tengo.UserFunction{
+		Name:  "find_process",
+		Value: osFindProcess,
+	}, // find_process(pid int) => imap(process)/error
+	"start_process": &tengo.UserFunction{
+		Name:  "start_process",
+		Value: osStartProcess,
+	}, // start_process(name string, argv array(string), dir string, env array(string)) => imap(process)/error
+	"exec_look_path": &tengo.UserFunction{
+		Name:  "exec_look_path",
+		Value: FuncASRSE(exec.LookPath),
+	}, // exec_look_path(file) => string/error
+	"exec": &tengo.UserFunction{
+		Name:  "exec",
+		Value: osExec,
+	}, // exec(name, args...) => command
+	"stat": &tengo.UserFunction{
+		Name:  "stat",
+		Value: osStat,
+	}, // stat(name) => imap(fileinfo)/error
+	"read_file": &tengo.UserFunction{
+		Name:  "read_file",
+		Value: osReadFile,
+	}, // readfile(name) => array(byte)/error
+}
+
+func osReadFile(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	fname, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	bytes, err := ioutil.ReadFile(fname)
+	if err != nil {
+		return wrapError(err), nil
+	}
+	if len(bytes) > tengo.MaxBytesLen {
+		return nil, tengo.ErrBytesLimit
+	}
+	return &tengo.Bytes{Value: bytes}, nil
+}
+
+func osStat(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	fname, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	stat, err := os.Stat(fname)
+	if err != nil {
+		return wrapError(err), nil
+	}
+	fstat := &tengo.ImmutableMap{
+		Value: map[string]tengo.Object{
+			"name":  &tengo.String{Value: stat.Name()},
+			"mtime": &tengo.Time{Value: stat.ModTime()},
+			"size":  &tengo.Int{Value: stat.Size()},
+			"mode":  &tengo.Int{Value: int64(stat.Mode())},
+		},
+	}
+	if stat.IsDir() {
+		fstat.Value["directory"] = tengo.TrueValue
+	} else {
+		fstat.Value["directory"] = tengo.FalseValue
+	}
+	return fstat, nil
+}
+
+func osCreate(args ...tengo.Object) (tengo.Object, error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	res, err := os.Create(s1)
+	if err != nil {
+		return wrapError(err), nil
+	}
+	return makeOSFile(res), nil
+}
+
+func osOpen(args ...tengo.Object) (tengo.Object, error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	res, err := os.Open(s1)
+	if err != nil {
+		return wrapError(err), nil
+	}
+	return makeOSFile(res), nil
+}
+
+func osOpenFile(args ...tengo.Object) (tengo.Object, error) {
+	if len(args) != 3 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+	}
+	i3, ok := tengo.ToInt(args[2])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "third",
+			Expected: "int(compatible)",
+			Found:    args[2].TypeName(),
+		}
+	}
+	res, err := os.OpenFile(s1, i2, os.FileMode(i3))
+	if err != nil {
+		return wrapError(err), nil
+	}
+	return makeOSFile(res), nil
+}
+
+func osArgs(args ...tengo.Object) (tengo.Object, error) {
+	if len(args) != 0 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	arr := &tengo.Array{}
+	for _, osArg := range os.Args {
+		if len(osArg) > tengo.MaxStringLen {
+			return nil, tengo.ErrStringLimit
+		}
+		arr.Value = append(arr.Value, &tengo.String{Value: osArg})
+	}
+	return arr, nil
+}
+
+func osFuncASFmRE(
+	name string,
+	fn func(string, os.FileMode) error,
+) *tengo.UserFunction {
+	return &tengo.UserFunction{
+		Name: name,
+		Value: func(args ...tengo.Object) (tengo.Object, error) {
+			if len(args) != 2 {
+				return nil, tengo.ErrWrongNumArguments
+			}
+			s1, ok := tengo.ToString(args[0])
+			if !ok {
+				return nil, tengo.ErrInvalidArgumentType{
+					Name:     "first",
+					Expected: "string(compatible)",
+					Found:    args[0].TypeName(),
+				}
+			}
+			i2, ok := tengo.ToInt64(args[1])
+			if !ok {
+				return nil, tengo.ErrInvalidArgumentType{
+					Name:     "second",
+					Expected: "int(compatible)",
+					Found:    args[1].TypeName(),
+				}
+			}
+			return wrapError(fn(s1, os.FileMode(i2))), nil
+		},
+	}
+}
+
+func osLookupEnv(args ...tengo.Object) (tengo.Object, error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	res, ok := os.LookupEnv(s1)
+	if !ok {
+		return tengo.FalseValue, nil
+	}
+	if len(res) > tengo.MaxStringLen {
+		return nil, tengo.ErrStringLimit
+	}
+	return &tengo.String{Value: res}, nil
+}
+
+func osExpandEnv(args ...tengo.Object) (tengo.Object, error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	var vlen int
+	var failed bool
+	s := os.Expand(s1, func(k string) string {
+		if failed {
+			return ""
+		}
+		v := os.Getenv(k)
+
+		// this does not count the other texts that are not being replaced
+		// but the code checks the final length at the end
+		vlen += len(v)
+		if vlen > tengo.MaxStringLen {
+			failed = true
+			return ""
+		}
+		return v
+	})
+	if failed || len(s) > tengo.MaxStringLen {
+		return nil, tengo.ErrStringLimit
+	}
+	return &tengo.String{Value: s}, nil
+}
+
+func osExec(args ...tengo.Object) (tengo.Object, error) {
+	if len(args) == 0 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	name, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	var execArgs []string
+	for idx, arg := range args[1:] {
+		execArg, ok := tengo.ToString(arg)
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     fmt.Sprintf("args[%d]", idx),
+				Expected: "string(compatible)",
+				Found:    args[1+idx].TypeName(),
+			}
+		}
+		execArgs = append(execArgs, execArg)
+	}
+	return makeOSExecCommand(exec.Command(name, execArgs...)), nil
+}
+
+func osFindProcess(args ...tengo.Object) (tengo.Object, error) {
+	if len(args) != 1 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	i1, ok := tengo.ToInt(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	proc, err := os.FindProcess(i1)
+	if err != nil {
+		return wrapError(err), nil
+	}
+	return makeOSProcess(proc), nil
+}
+
+func osStartProcess(args ...tengo.Object) (tengo.Object, error) {
+	if len(args) != 4 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+	name, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+	var argv []string
+	var err error
+	switch arg1 := args[1].(type) {
+	case *tengo.Array:
+		argv, err = stringArray(arg1.Value, "second")
+		if err != nil {
+			return nil, err
+		}
+	case *tengo.ImmutableArray:
+		argv, err = stringArray(arg1.Value, "second")
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "array",
+			Found:    arg1.TypeName(),
+		}
+	}
+
+	dir, ok := tengo.ToString(args[2])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "third",
+			Expected: "string(compatible)",
+			Found:    args[2].TypeName(),
+		}
+	}
+
+	var env []string
+	switch arg3 := args[3].(type) {
+	case *tengo.Array:
+		env, err = stringArray(arg3.Value, "fourth")
+		if err != nil {
+			return nil, err
+		}
+	case *tengo.ImmutableArray:
+		env, err = stringArray(arg3.Value, "fourth")
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "fourth",
+			Expected: "array",
+			Found:    arg3.TypeName(),
+		}
+	}
+
+	proc, err := os.StartProcess(name, argv, &os.ProcAttr{
+		Dir: dir,
+		Env: env,
+	})
+	if err != nil {
+		return wrapError(err), nil
+	}
+	return makeOSProcess(proc), nil
+}
+
+func stringArray(arr []tengo.Object, argName string) ([]string, error) {
+	var sarr []string
+	for idx, elem := range arr {
+		str, ok := elem.(*tengo.String)
+		if !ok {
+			return nil, tengo.ErrInvalidArgumentType{
+				Name:     fmt.Sprintf("%s[%d]", argName, idx),
+				Expected: "string",
+				Found:    elem.TypeName(),
+			}
+		}
+		sarr = append(sarr, str.Value)
+	}
+	return sarr, nil
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/os_exec.go b/vendor/github.com/d5/tengo/v2/stdlib/os_exec.go
new file mode 100644
index 00000000..7ee5c1cd
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/os_exec.go
@@ -0,0 +1,119 @@
+package stdlib
+
+import (
+	"os/exec"
+
+	"github.com/d5/tengo/v2"
+)
+
+func makeOSExecCommand(cmd *exec.Cmd) *tengo.ImmutableMap {
+	return &tengo.ImmutableMap{
+		Value: map[string]tengo.Object{
+			// combined_output() => bytes/error
+			"combined_output": &tengo.UserFunction{
+				Name:  "combined_output",
+				Value: FuncARYE(cmd.CombinedOutput),
+			},
+			// output() => bytes/error
+			"output": &tengo.UserFunction{
+				Name:  "output",
+				Value: FuncARYE(cmd.Output),
+			}, //
+			// run() => error
+			"run": &tengo.UserFunction{
+				Name:  "run",
+				Value: FuncARE(cmd.Run),
+			}, //
+			// start() => error
+			"start": &tengo.UserFunction{
+				Name:  "start",
+				Value: FuncARE(cmd.Start),
+			}, //
+			// wait() => error
+			"wait": &tengo.UserFunction{
+				Name:  "wait",
+				Value: FuncARE(cmd.Wait),
+			}, //
+			// set_path(path string)
+			"set_path": &tengo.UserFunction{
+				Name: "set_path",
+				Value: func(args ...tengo.Object) (tengo.Object, error) {
+					if len(args) != 1 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+					s1, ok := tengo.ToString(args[0])
+					if !ok {
+						return nil, tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "string(compatible)",
+							Found:    args[0].TypeName(),
+						}
+					}
+					cmd.Path = s1
+					return tengo.UndefinedValue, nil
+				},
+			},
+			// set_dir(dir string)
+			"set_dir": &tengo.UserFunction{
+				Name: "set_dir",
+				Value: func(args ...tengo.Object) (tengo.Object, error) {
+					if len(args) != 1 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+					s1, ok := tengo.ToString(args[0])
+					if !ok {
+						return nil, tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "string(compatible)",
+							Found:    args[0].TypeName(),
+						}
+					}
+					cmd.Dir = s1
+					return tengo.UndefinedValue, nil
+				},
+			},
+			// set_env(env array(string))
+			"set_env": &tengo.UserFunction{
+				Name: "set_env",
+				Value: func(args ...tengo.Object) (tengo.Object, error) {
+					if len(args) != 1 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+
+					var env []string
+					var err error
+					switch arg0 := args[0].(type) {
+					case *tengo.Array:
+						env, err = stringArray(arg0.Value, "first")
+						if err != nil {
+							return nil, err
+						}
+					case *tengo.ImmutableArray:
+						env, err = stringArray(arg0.Value, "first")
+						if err != nil {
+							return nil, err
+						}
+					default:
+						return nil, tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "array",
+							Found:    arg0.TypeName(),
+						}
+					}
+					cmd.Env = env
+					return tengo.UndefinedValue, nil
+				},
+			},
+			// process() => imap(process)
+			"process": &tengo.UserFunction{
+				Name: "process",
+				Value: func(args ...tengo.Object) (tengo.Object, error) {
+					if len(args) != 0 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+					return makeOSProcess(cmd.Process), nil
+				},
+			},
+		},
+	}
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/os_file.go b/vendor/github.com/d5/tengo/v2/stdlib/os_file.go
new file mode 100644
index 00000000..4f59b4c4
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/os_file.go
@@ -0,0 +1,117 @@
+package stdlib
+
+import (
+	"os"
+
+	"github.com/d5/tengo/v2"
+)
+
+func makeOSFile(file *os.File) *tengo.ImmutableMap {
+	return &tengo.ImmutableMap{
+		Value: map[string]tengo.Object{
+			// chdir() => true/error
+			"chdir": &tengo.UserFunction{
+				Name:  "chdir",
+				Value: FuncARE(file.Chdir),
+			}, //
+			// chown(uid int, gid int) => true/error
+			"chown": &tengo.UserFunction{
+				Name:  "chown",
+				Value: FuncAIIRE(file.Chown),
+			}, //
+			// close() => error
+			"close": &tengo.UserFunction{
+				Name:  "close",
+				Value: FuncARE(file.Close),
+			}, //
+			// name() => string
+			"name": &tengo.UserFunction{
+				Name:  "name",
+				Value: FuncARS(file.Name),
+			}, //
+			// readdirnames(n int) => array(string)/error
+			"readdirnames": &tengo.UserFunction{
+				Name:  "readdirnames",
+				Value: FuncAIRSsE(file.Readdirnames),
+			}, //
+			// sync() => error
+			"sync": &tengo.UserFunction{
+				Name:  "sync",
+				Value: FuncARE(file.Sync),
+			}, //
+			// write(bytes) => int/error
+			"write": &tengo.UserFunction{
+				Name:  "write",
+				Value: FuncAYRIE(file.Write),
+			}, //
+			// write(string) => int/error
+			"write_string": &tengo.UserFunction{
+				Name:  "write_string",
+				Value: FuncASRIE(file.WriteString),
+			}, //
+			// read(bytes) => int/error
+			"read": &tengo.UserFunction{
+				Name:  "read",
+				Value: FuncAYRIE(file.Read),
+			}, //
+			// chmod(mode int) => error
+			"chmod": &tengo.UserFunction{
+				Name: "chmod",
+				Value: func(args ...tengo.Object) (tengo.Object, error) {
+					if len(args) != 1 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+					i1, ok := tengo.ToInt64(args[0])
+					if !ok {
+						return nil, tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "int(compatible)",
+							Found:    args[0].TypeName(),
+						}
+					}
+					return wrapError(file.Chmod(os.FileMode(i1))), nil
+				},
+			},
+			// seek(offset int, whence int) => int/error
+			"seek": &tengo.UserFunction{
+				Name: "seek",
+				Value: func(args ...tengo.Object) (tengo.Object, error) {
+					if len(args) != 2 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+					i1, ok := tengo.ToInt64(args[0])
+					if !ok {
+						return nil, tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "int(compatible)",
+							Found:    args[0].TypeName(),
+						}
+					}
+					i2, ok := tengo.ToInt(args[1])
+					if !ok {
+						return nil, tengo.ErrInvalidArgumentType{
+							Name:     "second",
+							Expected: "int(compatible)",
+							Found:    args[1].TypeName(),
+						}
+					}
+					res, err := file.Seek(i1, i2)
+					if err != nil {
+						return wrapError(err), nil
+					}
+					return &tengo.Int{Value: res}, nil
+				},
+			},
+			// stat() => imap(fileinfo)/error
+			"stat": &tengo.UserFunction{
+				Name: "stat",
+				Value: func(args ...tengo.Object) (tengo.Object, error) {
+					if len(args) != 0 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+					return osStat(&tengo.String{Value: file.Name()})
+				},
+			},
+		},
+	}
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/os_process.go b/vendor/github.com/d5/tengo/v2/stdlib/os_process.go
new file mode 100644
index 00000000..7fcf27a4
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/os_process.go
@@ -0,0 +1,76 @@
+package stdlib
+
+import (
+	"os"
+	"syscall"
+
+	"github.com/d5/tengo/v2"
+)
+
+func makeOSProcessState(state *os.ProcessState) *tengo.ImmutableMap {
+	return &tengo.ImmutableMap{
+		Value: map[string]tengo.Object{
+			"exited": &tengo.UserFunction{
+				Name:  "exited",
+				Value: FuncARB(state.Exited),
+			},
+			"pid": &tengo.UserFunction{
+				Name:  "pid",
+				Value: FuncARI(state.Pid),
+			},
+			"string": &tengo.UserFunction{
+				Name:  "string",
+				Value: FuncARS(state.String),
+			},
+			"success": &tengo.UserFunction{
+				Name:  "success",
+				Value: FuncARB(state.Success),
+			},
+		},
+	}
+}
+
+func makeOSProcess(proc *os.Process) *tengo.ImmutableMap {
+	return &tengo.ImmutableMap{
+		Value: map[string]tengo.Object{
+			"kill": &tengo.UserFunction{
+				Name:  "kill",
+				Value: FuncARE(proc.Kill),
+			},
+			"release": &tengo.UserFunction{
+				Name:  "release",
+				Value: FuncARE(proc.Release),
+			},
+			"signal": &tengo.UserFunction{
+				Name: "signal",
+				Value: func(args ...tengo.Object) (tengo.Object, error) {
+					if len(args) != 1 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+					i1, ok := tengo.ToInt64(args[0])
+					if !ok {
+						return nil, tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "int(compatible)",
+							Found:    args[0].TypeName(),
+						}
+					}
+					return wrapError(proc.Signal(syscall.Signal(i1))), nil
+				},
+			},
+			"wait": &tengo.UserFunction{
+				Name: "wait",
+				Value: func(args ...tengo.Object) (tengo.Object, error) {
+					if len(args) != 0 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+					state, err := proc.Wait()
+					if err != nil {
+						return wrapError(err), nil
+					}
+					return makeOSProcessState(state), nil
+				},
+			},
+		},
+	}
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/rand.go b/vendor/github.com/d5/tengo/v2/stdlib/rand.go
new file mode 100644
index 00000000..5d21e1df
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/rand.go
@@ -0,0 +1,138 @@
+package stdlib
+
+import (
+	"math/rand"
+
+	"github.com/d5/tengo/v2"
+)
+
+var randModule = map[string]tengo.Object{
+	"int": &tengo.UserFunction{
+		Name:  "int",
+		Value: FuncARI64(rand.Int63),
+	},
+	"float": &tengo.UserFunction{
+		Name:  "float",
+		Value: FuncARF(rand.Float64),
+	},
+	"intn": &tengo.UserFunction{
+		Name:  "intn",
+		Value: FuncAI64RI64(rand.Int63n),
+	},
+	"exp_float": &tengo.UserFunction{
+		Name:  "exp_float",
+		Value: FuncARF(rand.ExpFloat64),
+	},
+	"norm_float": &tengo.UserFunction{
+		Name:  "norm_float",
+		Value: FuncARF(rand.NormFloat64),
+	},
+	"perm": &tengo.UserFunction{
+		Name:  "perm",
+		Value: FuncAIRIs(rand.Perm),
+	},
+	"seed": &tengo.UserFunction{
+		Name:  "seed",
+		Value: FuncAI64R(rand.Seed),
+	},
+	"read": &tengo.UserFunction{
+		Name: "read",
+		Value: func(args ...tengo.Object) (ret tengo.Object, err error) {
+			if len(args) != 1 {
+				return nil, tengo.ErrWrongNumArguments
+			}
+			y1, ok := args[0].(*tengo.Bytes)
+			if !ok {
+				return nil, tengo.ErrInvalidArgumentType{
+					Name:     "first",
+					Expected: "bytes",
+					Found:    args[0].TypeName(),
+				}
+			}
+			res, err := rand.Read(y1.Value)
+			if err != nil {
+				ret = wrapError(err)
+				return
+			}
+			return &tengo.Int{Value: int64(res)}, nil
+		},
+	},
+	"rand": &tengo.UserFunction{
+		Name: "rand",
+		Value: func(args ...tengo.Object) (tengo.Object, error) {
+			if len(args) != 1 {
+				return nil, tengo.ErrWrongNumArguments
+			}
+			i1, ok := tengo.ToInt64(args[0])
+			if !ok {
+				return nil, tengo.ErrInvalidArgumentType{
+					Name:     "first",
+					Expected: "int(compatible)",
+					Found:    args[0].TypeName(),
+				}
+			}
+			src := rand.NewSource(i1)
+			return randRand(rand.New(src)), nil
+		},
+	},
+}
+
+func randRand(r *rand.Rand) *tengo.ImmutableMap {
+	return &tengo.ImmutableMap{
+		Value: map[string]tengo.Object{
+			"int": &tengo.UserFunction{
+				Name:  "int",
+				Value: FuncARI64(r.Int63),
+			},
+			"float": &tengo.UserFunction{
+				Name:  "float",
+				Value: FuncARF(r.Float64),
+			},
+			"intn": &tengo.UserFunction{
+				Name:  "intn",
+				Value: FuncAI64RI64(r.Int63n),
+			},
+			"exp_float": &tengo.UserFunction{
+				Name:  "exp_float",
+				Value: FuncARF(r.ExpFloat64),
+			},
+			"norm_float": &tengo.UserFunction{
+				Name:  "norm_float",
+				Value: FuncARF(r.NormFloat64),
+			},
+			"perm": &tengo.UserFunction{
+				Name:  "perm",
+				Value: FuncAIRIs(r.Perm),
+			},
+			"seed": &tengo.UserFunction{
+				Name:  "seed",
+				Value: FuncAI64R(r.Seed),
+			},
+			"read": &tengo.UserFunction{
+				Name: "read",
+				Value: func(args ...tengo.Object) (
+					ret tengo.Object,
+					err error,
+				) {
+					if len(args) != 1 {
+						return nil, tengo.ErrWrongNumArguments
+					}
+					y1, ok := args[0].(*tengo.Bytes)
+					if !ok {
+						return nil, tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "bytes",
+							Found:    args[0].TypeName(),
+						}
+					}
+					res, err := r.Read(y1.Value)
+					if err != nil {
+						ret = wrapError(err)
+						return
+					}
+					return &tengo.Int{Value: int64(res)}, nil
+				},
+			},
+		},
+	}
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/source_modules.go b/vendor/github.com/d5/tengo/v2/stdlib/source_modules.go
new file mode 100644
index 00000000..ca69d7d1
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/source_modules.go
@@ -0,0 +1,8 @@
+// Code generated using gensrcmods.go; DO NOT EDIT.
+
+package stdlib
+
+// SourceModules are source type standard library modules.
+var SourceModules = map[string]string{
+	"enum": "is_enumerable := func(x) {\n  return is_array(x) || is_map(x) || is_immutable_array(x) || is_immutable_map(x)\n}\n\nis_array_like := func(x) {\n  return is_array(x) || is_immutable_array(x)\n}\n\nexport {\n  // all returns true if the given function `fn` evaluates to a truthy value on\n  // all of the items in `x`. It returns undefined if `x` is not enumerable.\n  all: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      if !fn(k, v) { return false }\n    }\n\n    return true\n  },\n  // any returns true if the given function `fn` evaluates to a truthy value on\n  // any of the items in `x`. It returns undefined if `x` is not enumerable.\n  any: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      if fn(k, v) { return true }\n    }\n\n    return false\n  },\n  // chunk returns an array of elements split into groups the length of size.\n  // If `x` can't be split evenly, the final chunk will be the remaining elements.\n  // It returns undefined if `x` is not array.\n  chunk: func(x, size) {\n    if !is_array_like(x) || !size { return undefined }\n\n    numElements := len(x)\n    if !numElements { return [] }\n\n    res := []\n    idx := 0\n    for idx < numElements {\n      res = append(res, x[idx:idx+size])\n      idx += size\n    }\n\n    return res\n  },\n  // at returns an element at the given index (if `x` is array) or\n  // key (if `x` is map). It returns undefined if `x` is not enumerable.\n  at: func(x, key) {\n    if !is_enumerable(x) { return undefined }\n\n    if is_array_like(x) {\n        if !is_int(key) { return undefined }\n    } else {\n        if !is_string(key) { return undefined }\n    }\n\n    return x[key]\n  },\n  // each iterates over elements of `x` and invokes `fn` for each element. `fn` is\n  // invoked with two arguments: `key` and `value`. `key` is an int index\n  // if `x` is array. `key` is a string key if `x` is map. It does not iterate\n  // and returns undefined if `x` is not enumerable.\n  each: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      fn(k, v)\n    }\n  },\n  // filter iterates over elements of `x`, returning an array of all elements `fn`\n  // returns truthy for. `fn` is invoked with two arguments: `key` and `value`.\n  // `key` is an int index if `x` is array. `key` is a string key if `x` is map.\n  // It returns undefined if `x` is not enumerable.\n  filter: func(x, fn) {\n    if !is_array_like(x) { return undefined }\n\n    dst := []\n    for k, v in x {\n      if fn(k, v) { dst = append(dst, v) }\n    }\n\n    return dst\n  },\n  // find iterates over elements of `x`, returning value of the first element `fn`\n  // returns truthy for. `fn` is invoked with two arguments: `key` and `value`.\n  // `key` is an int index if `x` is array. `key` is a string key if `x` is map.\n  // It returns undefined if `x` is not enumerable.\n  find: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      if fn(k, v) { return v }\n    }\n  },\n  // find_key iterates over elements of `x`, returning key or index of the first\n  // element `fn` returns truthy for. `fn` is invoked with two arguments: `key`\n  // and `value`. `key` is an int index if `x` is array. `key` is a string key if\n  // `x` is map. It returns undefined if `x` is not enumerable.\n  find_key: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      if fn(k, v) { return k }\n    }\n  },\n  // map creates an array of values by running each element in `x` through `fn`.\n  // `fn` is invoked with two arguments: `key` and `value`. `key` is an int index\n  // if `x` is array. `key` is a string key if `x` is map. It returns undefined\n  // if `x` is not enumerable.\n  map: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    dst := []\n    for k, v in x {\n      dst = append(dst, fn(k, v))\n    }\n\n    return dst\n  },\n  // key returns the first argument.\n  key: func(k, _) { return k },\n  // value returns the second argument.\n  value: func(_, v) { return v }\n}\n",
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/srcmod_enum.tengo b/vendor/github.com/d5/tengo/v2/stdlib/srcmod_enum.tengo
new file mode 100644
index 00000000..7a5ea637
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/srcmod_enum.tengo
@@ -0,0 +1,128 @@
+is_enumerable := func(x) {
+  return is_array(x) || is_map(x) || is_immutable_array(x) || is_immutable_map(x)
+}
+
+is_array_like := func(x) {
+  return is_array(x) || is_immutable_array(x)
+}
+
+export {
+  // all returns true if the given function `fn` evaluates to a truthy value on
+  // all of the items in `x`. It returns undefined if `x` is not enumerable.
+  all: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      if !fn(k, v) { return false }
+    }
+
+    return true
+  },
+  // any returns true if the given function `fn` evaluates to a truthy value on
+  // any of the items in `x`. It returns undefined if `x` is not enumerable.
+  any: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      if fn(k, v) { return true }
+    }
+
+    return false
+  },
+  // chunk returns an array of elements split into groups the length of size.
+  // If `x` can't be split evenly, the final chunk will be the remaining elements.
+  // It returns undefined if `x` is not array.
+  chunk: func(x, size) {
+    if !is_array_like(x) || !size { return undefined }
+
+    numElements := len(x)
+    if !numElements { return [] }
+
+    res := []
+    idx := 0
+    for idx < numElements {
+      res = append(res, x[idx:idx+size])
+      idx += size
+    }
+
+    return res
+  },
+  // at returns an element at the given index (if `x` is array) or
+  // key (if `x` is map). It returns undefined if `x` is not enumerable.
+  at: func(x, key) {
+    if !is_enumerable(x) { return undefined }
+
+    if is_array_like(x) {
+        if !is_int(key) { return undefined }
+    } else {
+        if !is_string(key) { return undefined }
+    }
+
+    return x[key]
+  },
+  // each iterates over elements of `x` and invokes `fn` for each element. `fn` is
+  // invoked with two arguments: `key` and `value`. `key` is an int index
+  // if `x` is array. `key` is a string key if `x` is map. It does not iterate
+  // and returns undefined if `x` is not enumerable.
+  each: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      fn(k, v)
+    }
+  },
+  // filter iterates over elements of `x`, returning an array of all elements `fn`
+  // returns truthy for. `fn` is invoked with two arguments: `key` and `value`.
+  // `key` is an int index if `x` is array. `key` is a string key if `x` is map.
+  // It returns undefined if `x` is not enumerable.
+  filter: func(x, fn) {
+    if !is_array_like(x) { return undefined }
+
+    dst := []
+    for k, v in x {
+      if fn(k, v) { dst = append(dst, v) }
+    }
+
+    return dst
+  },
+  // find iterates over elements of `x`, returning value of the first element `fn`
+  // returns truthy for. `fn` is invoked with two arguments: `key` and `value`.
+  // `key` is an int index if `x` is array. `key` is a string key if `x` is map.
+  // It returns undefined if `x` is not enumerable.
+  find: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      if fn(k, v) { return v }
+    }
+  },
+  // find_key iterates over elements of `x`, returning key or index of the first
+  // element `fn` returns truthy for. `fn` is invoked with two arguments: `key`
+  // and `value`. `key` is an int index if `x` is array. `key` is a string key if
+  // `x` is map. It returns undefined if `x` is not enumerable.
+  find_key: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      if fn(k, v) { return k }
+    }
+  },
+  // map creates an array of values by running each element in `x` through `fn`.
+  // `fn` is invoked with two arguments: `key` and `value`. `key` is an int index
+  // if `x` is array. `key` is a string key if `x` is map. It returns undefined
+  // if `x` is not enumerable.
+  map: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    dst := []
+    for k, v in x {
+      dst = append(dst, fn(k, v))
+    }
+
+    return dst
+  },
+  // key returns the first argument.
+  key: func(k, _) { return k },
+  // value returns the second argument.
+  value: func(_, v) { return v }
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/stdlib.go b/vendor/github.com/d5/tengo/v2/stdlib/stdlib.go
new file mode 100644
index 00000000..16c369a0
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/stdlib.go
@@ -0,0 +1,34 @@
+package stdlib
+
+//go:generate go run gensrcmods.go
+
+import (
+	"github.com/d5/tengo/v2"
+)
+
+// AllModuleNames returns a list of all default module names.
+func AllModuleNames() []string {
+	var names []string
+	for name := range BuiltinModules {
+		names = append(names, name)
+	}
+	for name := range SourceModules {
+		names = append(names, name)
+	}
+	return names
+}
+
+// GetModuleMap returns the module map that includes all modules
+// for the given module names.
+func GetModuleMap(names ...string) *tengo.ModuleMap {
+	modules := tengo.NewModuleMap()
+	for _, name := range names {
+		if mod := BuiltinModules[name]; mod != nil {
+			modules.AddBuiltinModule(name, mod)
+		}
+		if mod := SourceModules[name]; mod != "" {
+			modules.AddSourceModule(name, []byte(mod))
+		}
+	}
+	return modules
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/text.go b/vendor/github.com/d5/tengo/v2/stdlib/text.go
new file mode 100644
index 00000000..d7d5d1da
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/text.go
@@ -0,0 +1,1072 @@
+package stdlib
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+	"unicode/utf8"
+
+	"github.com/d5/tengo/v2"
+)
+
+var textModule = map[string]tengo.Object{
+	"re_match": &tengo.UserFunction{
+		Name:  "re_match",
+		Value: textREMatch,
+	}, // re_match(pattern, text) => bool/error
+	"re_find": &tengo.UserFunction{
+		Name:  "re_find",
+		Value: textREFind,
+	}, // re_find(pattern, text, count) => [[{text:,begin:,end:}]]/undefined
+	"re_replace": &tengo.UserFunction{
+		Name:  "re_replace",
+		Value: textREReplace,
+	}, // re_replace(pattern, text, repl) => string/error
+	"re_split": &tengo.UserFunction{
+		Name:  "re_split",
+		Value: textRESplit,
+	}, // re_split(pattern, text, count) => [string]/error
+	"re_compile": &tengo.UserFunction{
+		Name:  "re_compile",
+		Value: textRECompile,
+	}, // re_compile(pattern) => Regexp/error
+	"compare": &tengo.UserFunction{
+		Name:  "compare",
+		Value: FuncASSRI(strings.Compare),
+	}, // compare(a, b) => int
+	"contains": &tengo.UserFunction{
+		Name:  "contains",
+		Value: FuncASSRB(strings.Contains),
+	}, // contains(s, substr) => bool
+	"contains_any": &tengo.UserFunction{
+		Name:  "contains_any",
+		Value: FuncASSRB(strings.ContainsAny),
+	}, // contains_any(s, chars) => bool
+	"count": &tengo.UserFunction{
+		Name:  "count",
+		Value: FuncASSRI(strings.Count),
+	}, // count(s, substr) => int
+	"equal_fold": &tengo.UserFunction{
+		Name:  "equal_fold",
+		Value: FuncASSRB(strings.EqualFold),
+	}, // "equal_fold(s, t) => bool
+	"fields": &tengo.UserFunction{
+		Name:  "fields",
+		Value: FuncASRSs(strings.Fields),
+	}, // fields(s) => [string]
+	"has_prefix": &tengo.UserFunction{
+		Name:  "has_prefix",
+		Value: FuncASSRB(strings.HasPrefix),
+	}, // has_prefix(s, prefix) => bool
+	"has_suffix": &tengo.UserFunction{
+		Name:  "has_suffix",
+		Value: FuncASSRB(strings.HasSuffix),
+	}, // has_suffix(s, suffix) => bool
+	"index": &tengo.UserFunction{
+		Name:  "index",
+		Value: FuncASSRI(strings.Index),
+	}, // index(s, substr) => int
+	"index_any": &tengo.UserFunction{
+		Name:  "index_any",
+		Value: FuncASSRI(strings.IndexAny),
+	}, // index_any(s, chars) => int
+	"join": &tengo.UserFunction{
+		Name:  "join",
+		Value: textJoin,
+	}, // join(arr, sep) => string
+	"last_index": &tengo.UserFunction{
+		Name:  "last_index",
+		Value: FuncASSRI(strings.LastIndex),
+	}, // last_index(s, substr) => int
+	"last_index_any": &tengo.UserFunction{
+		Name:  "last_index_any",
+		Value: FuncASSRI(strings.LastIndexAny),
+	}, // last_index_any(s, chars) => int
+	"repeat": &tengo.UserFunction{
+		Name:  "repeat",
+		Value: textRepeat,
+	}, // repeat(s, count) => string
+	"replace": &tengo.UserFunction{
+		Name:  "replace",
+		Value: textReplace,
+	}, // replace(s, old, new, n) => string
+	"substr": &tengo.UserFunction{
+		Name:  "substr",
+		Value: textSubstring,
+	}, // substr(s, lower, upper) => string
+	"split": &tengo.UserFunction{
+		Name:  "split",
+		Value: FuncASSRSs(strings.Split),
+	}, // split(s, sep) => [string]
+	"split_after": &tengo.UserFunction{
+		Name:  "split_after",
+		Value: FuncASSRSs(strings.SplitAfter),
+	}, // split_after(s, sep) => [string]
+	"split_after_n": &tengo.UserFunction{
+		Name:  "split_after_n",
+		Value: FuncASSIRSs(strings.SplitAfterN),
+	}, // split_after_n(s, sep, n) => [string]
+	"split_n": &tengo.UserFunction{
+		Name:  "split_n",
+		Value: FuncASSIRSs(strings.SplitN),
+	}, // split_n(s, sep, n) => [string]
+	"title": &tengo.UserFunction{
+		Name:  "title",
+		Value: FuncASRS(strings.Title),
+	}, // title(s) => string
+	"to_lower": &tengo.UserFunction{
+		Name:  "to_lower",
+		Value: FuncASRS(strings.ToLower),
+	}, // to_lower(s) => string
+	"to_title": &tengo.UserFunction{
+		Name:  "to_title",
+		Value: FuncASRS(strings.ToTitle),
+	}, // to_title(s) => string
+	"to_upper": &tengo.UserFunction{
+		Name:  "to_upper",
+		Value: FuncASRS(strings.ToUpper),
+	}, // to_upper(s) => string
+	"pad_left": &tengo.UserFunction{
+		Name:  "pad_left",
+		Value: textPadLeft,
+	}, // pad_left(s, pad_len, pad_with) => string
+	"pad_right": &tengo.UserFunction{
+		Name:  "pad_right",
+		Value: textPadRight,
+	}, // pad_right(s, pad_len, pad_with) => string
+	"trim": &tengo.UserFunction{
+		Name:  "trim",
+		Value: FuncASSRS(strings.Trim),
+	}, // trim(s, cutset) => string
+	"trim_left": &tengo.UserFunction{
+		Name:  "trim_left",
+		Value: FuncASSRS(strings.TrimLeft),
+	}, // trim_left(s, cutset) => string
+	"trim_prefix": &tengo.UserFunction{
+		Name:  "trim_prefix",
+		Value: FuncASSRS(strings.TrimPrefix),
+	}, // trim_prefix(s, prefix) => string
+	"trim_right": &tengo.UserFunction{
+		Name:  "trim_right",
+		Value: FuncASSRS(strings.TrimRight),
+	}, // trim_right(s, cutset) => string
+	"trim_space": &tengo.UserFunction{
+		Name:  "trim_space",
+		Value: FuncASRS(strings.TrimSpace),
+	}, // trim_space(s) => string
+	"trim_suffix": &tengo.UserFunction{
+		Name:  "trim_suffix",
+		Value: FuncASSRS(strings.TrimSuffix),
+	}, // trim_suffix(s, suffix) => string
+	"atoi": &tengo.UserFunction{
+		Name:  "atoi",
+		Value: FuncASRIE(strconv.Atoi),
+	}, // atoi(str) => int/error
+	"format_bool": &tengo.UserFunction{
+		Name:  "format_bool",
+		Value: textFormatBool,
+	}, // format_bool(b) => string
+	"format_float": &tengo.UserFunction{
+		Name:  "format_float",
+		Value: textFormatFloat,
+	}, // format_float(f, fmt, prec, bits) => string
+	"format_int": &tengo.UserFunction{
+		Name:  "format_int",
+		Value: textFormatInt,
+	}, // format_int(i, base) => string
+	"itoa": &tengo.UserFunction{
+		Name:  "itoa",
+		Value: FuncAIRS(strconv.Itoa),
+	}, // itoa(i) => string
+	"parse_bool": &tengo.UserFunction{
+		Name:  "parse_bool",
+		Value: textParseBool,
+	}, // parse_bool(str) => bool/error
+	"parse_float": &tengo.UserFunction{
+		Name:  "parse_float",
+		Value: textParseFloat,
+	}, // parse_float(str, bits) => float/error
+	"parse_int": &tengo.UserFunction{
+		Name:  "parse_int",
+		Value: textParseInt,
+	}, // parse_int(str, base, bits) => int/error
+	"quote": &tengo.UserFunction{
+		Name:  "quote",
+		Value: FuncASRS(strconv.Quote),
+	}, // quote(str) => string
+	"unquote": &tengo.UserFunction{
+		Name:  "unquote",
+		Value: FuncASRSE(strconv.Unquote),
+	}, // unquote(str) => string/error
+}
+
+func textREMatch(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	s2, ok := tengo.ToString(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	matched, err := regexp.MatchString(s1, s2)
+	if err != nil {
+		ret = wrapError(err)
+		return
+	}
+
+	if matched {
+		ret = tengo.TrueValue
+	} else {
+		ret = tengo.FalseValue
+	}
+
+	return
+}
+
+func textREFind(args ...tengo.Object) (ret tengo.Object, err error) {
+	numArgs := len(args)
+	if numArgs != 2 && numArgs != 3 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	re, err := regexp.Compile(s1)
+	if err != nil {
+		ret = wrapError(err)
+		return
+	}
+
+	s2, ok := tengo.ToString(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	if numArgs < 3 {
+		m := re.FindStringSubmatchIndex(s2)
+		if m == nil {
+			ret = tengo.UndefinedValue
+			return
+		}
+
+		arr := &tengo.Array{}
+		for i := 0; i < len(m); i += 2 {
+			arr.Value = append(arr.Value,
+				&tengo.ImmutableMap{Value: map[string]tengo.Object{
+					"text":  &tengo.String{Value: s2[m[i]:m[i+1]]},
+					"begin": &tengo.Int{Value: int64(m[i])},
+					"end":   &tengo.Int{Value: int64(m[i+1])},
+				}})
+		}
+
+		ret = &tengo.Array{Value: []tengo.Object{arr}}
+
+		return
+	}
+
+	i3, ok := tengo.ToInt(args[2])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "third",
+			Expected: "int(compatible)",
+			Found:    args[2].TypeName(),
+		}
+		return
+	}
+	m := re.FindAllStringSubmatchIndex(s2, i3)
+	if m == nil {
+		ret = tengo.UndefinedValue
+		return
+	}
+
+	arr := &tengo.Array{}
+	for _, m := range m {
+		subMatch := &tengo.Array{}
+		for i := 0; i < len(m); i += 2 {
+			subMatch.Value = append(subMatch.Value,
+				&tengo.ImmutableMap{Value: map[string]tengo.Object{
+					"text":  &tengo.String{Value: s2[m[i]:m[i+1]]},
+					"begin": &tengo.Int{Value: int64(m[i])},
+					"end":   &tengo.Int{Value: int64(m[i+1])},
+				}})
+		}
+
+		arr.Value = append(arr.Value, subMatch)
+	}
+
+	ret = arr
+
+	return
+}
+
+func textREReplace(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 3 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	s2, ok := tengo.ToString(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	s3, ok := tengo.ToString(args[2])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "third",
+			Expected: "string(compatible)",
+			Found:    args[2].TypeName(),
+		}
+		return
+	}
+
+	re, err := regexp.Compile(s1)
+	if err != nil {
+		ret = wrapError(err)
+	} else {
+		s, ok := doTextRegexpReplace(re, s2, s3)
+		if !ok {
+			return nil, tengo.ErrStringLimit
+		}
+
+		ret = &tengo.String{Value: s}
+	}
+
+	return
+}
+
+func textRESplit(args ...tengo.Object) (ret tengo.Object, err error) {
+	numArgs := len(args)
+	if numArgs != 2 && numArgs != 3 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	s2, ok := tengo.ToString(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	var i3 = -1
+	if numArgs > 2 {
+		i3, ok = tengo.ToInt(args[2])
+		if !ok {
+			err = tengo.ErrInvalidArgumentType{
+				Name:     "third",
+				Expected: "int(compatible)",
+				Found:    args[2].TypeName(),
+			}
+			return
+		}
+	}
+
+	re, err := regexp.Compile(s1)
+	if err != nil {
+		ret = wrapError(err)
+		return
+	}
+
+	arr := &tengo.Array{}
+	for _, s := range re.Split(s2, i3) {
+		arr.Value = append(arr.Value, &tengo.String{Value: s})
+	}
+
+	ret = arr
+
+	return
+}
+
+func textRECompile(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	re, err := regexp.Compile(s1)
+	if err != nil {
+		ret = wrapError(err)
+	} else {
+		ret = makeTextRegexp(re)
+	}
+
+	return
+}
+
+func textReplace(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 4 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	s2, ok := tengo.ToString(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	s3, ok := tengo.ToString(args[2])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "third",
+			Expected: "string(compatible)",
+			Found:    args[2].TypeName(),
+		}
+		return
+	}
+
+	i4, ok := tengo.ToInt(args[3])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "fourth",
+			Expected: "int(compatible)",
+			Found:    args[3].TypeName(),
+		}
+		return
+	}
+
+	s, ok := doTextReplace(s1, s2, s3, i4)
+	if !ok {
+		err = tengo.ErrStringLimit
+		return
+	}
+
+	ret = &tengo.String{Value: s}
+
+	return
+}
+
+func textSubstring(args ...tengo.Object) (ret tengo.Object, err error) {
+	argslen := len(args)
+	if argslen != 2 && argslen != 3 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	strlen := len(s1)
+	i3 := strlen
+	if argslen == 3 {
+		i3, ok = tengo.ToInt(args[2])
+		if !ok {
+			err = tengo.ErrInvalidArgumentType{
+				Name:     "third",
+				Expected: "int(compatible)",
+				Found:    args[2].TypeName(),
+			}
+			return
+		}
+	}
+
+	if i2 > i3 {
+		err = tengo.ErrInvalidIndexType
+		return
+	}
+
+	if i2 < 0 {
+		i2 = 0
+	} else if i2 > strlen {
+		i2 = strlen
+	}
+
+	if i3 < 0 {
+		i3 = 0
+	} else if i3 > strlen {
+		i3 = strlen
+	}
+
+	ret = &tengo.String{Value: s1[i2:i3]}
+
+	return
+}
+
+func textPadLeft(args ...tengo.Object) (ret tengo.Object, err error) {
+	argslen := len(args)
+	if argslen != 2 && argslen != 3 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	if i2 > tengo.MaxStringLen {
+		return nil, tengo.ErrStringLimit
+	}
+
+	sLen := len(s1)
+	if sLen >= i2 {
+		ret = &tengo.String{Value: s1}
+		return
+	}
+
+	s3 := " "
+	if argslen == 3 {
+		s3, ok = tengo.ToString(args[2])
+		if !ok {
+			err = tengo.ErrInvalidArgumentType{
+				Name:     "third",
+				Expected: "string(compatible)",
+				Found:    args[2].TypeName(),
+			}
+			return
+		}
+	}
+
+	padStrLen := len(s3)
+	if padStrLen == 0 {
+		ret = &tengo.String{Value: s1}
+		return
+	}
+
+	padCount := ((i2 - padStrLen) / padStrLen) + 1
+	retStr := strings.Repeat(s3, padCount) + s1
+	ret = &tengo.String{Value: retStr[len(retStr)-i2:]}
+
+	return
+}
+
+func textPadRight(args ...tengo.Object) (ret tengo.Object, err error) {
+	argslen := len(args)
+	if argslen != 2 && argslen != 3 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	if i2 > tengo.MaxStringLen {
+		return nil, tengo.ErrStringLimit
+	}
+
+	sLen := len(s1)
+	if sLen >= i2 {
+		ret = &tengo.String{Value: s1}
+		return
+	}
+
+	s3 := " "
+	if argslen == 3 {
+		s3, ok = tengo.ToString(args[2])
+		if !ok {
+			err = tengo.ErrInvalidArgumentType{
+				Name:     "third",
+				Expected: "string(compatible)",
+				Found:    args[2].TypeName(),
+			}
+			return
+		}
+	}
+
+	padStrLen := len(s3)
+	if padStrLen == 0 {
+		ret = &tengo.String{Value: s1}
+		return
+	}
+
+	padCount := ((i2 - padStrLen) / padStrLen) + 1
+	retStr := s1 + strings.Repeat(s3, padCount)
+	ret = &tengo.String{Value: retStr[:i2]}
+
+	return
+}
+
+func textRepeat(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+	}
+
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+	}
+
+	if len(s1)*i2 > tengo.MaxStringLen {
+		return nil, tengo.ErrStringLimit
+	}
+
+	return &tengo.String{Value: strings.Repeat(s1, i2)}, nil
+}
+
+func textJoin(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		return nil, tengo.ErrWrongNumArguments
+	}
+
+	var slen int
+	var ss1 []string
+	switch arg0 := args[0].(type) {
+	case *tengo.Array:
+		for idx, a := range arg0.Value {
+			as, ok := tengo.ToString(a)
+			if !ok {
+				return nil, tengo.ErrInvalidArgumentType{
+					Name:     fmt.Sprintf("first[%d]", idx),
+					Expected: "string(compatible)",
+					Found:    a.TypeName(),
+				}
+			}
+			slen += len(as)
+			ss1 = append(ss1, as)
+		}
+	case *tengo.ImmutableArray:
+		for idx, a := range arg0.Value {
+			as, ok := tengo.ToString(a)
+			if !ok {
+				return nil, tengo.ErrInvalidArgumentType{
+					Name:     fmt.Sprintf("first[%d]", idx),
+					Expected: "string(compatible)",
+					Found:    a.TypeName(),
+				}
+			}
+			slen += len(as)
+			ss1 = append(ss1, as)
+		}
+	default:
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "array",
+			Found:    args[0].TypeName(),
+		}
+	}
+
+	s2, ok := tengo.ToString(args[1])
+	if !ok {
+		return nil, tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+	}
+
+	// make sure output length does not exceed the limit
+	if slen+len(s2)*(len(ss1)-1) > tengo.MaxStringLen {
+		return nil, tengo.ErrStringLimit
+	}
+
+	return &tengo.String{Value: strings.Join(ss1, s2)}, nil
+}
+
+func textFormatBool(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	b1, ok := args[0].(*tengo.Bool)
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "bool",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	if b1 == tengo.TrueValue {
+		ret = &tengo.String{Value: "true"}
+	} else {
+		ret = &tengo.String{Value: "false"}
+	}
+
+	return
+}
+
+func textFormatFloat(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 4 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	f1, ok := args[0].(*tengo.Float)
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "float",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	s2, ok := tengo.ToString(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	i3, ok := tengo.ToInt(args[2])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "third",
+			Expected: "int(compatible)",
+			Found:    args[2].TypeName(),
+		}
+		return
+	}
+
+	i4, ok := tengo.ToInt(args[3])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "fourth",
+			Expected: "int(compatible)",
+			Found:    args[3].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.String{Value: strconv.FormatFloat(f1.Value, s2[0], i3, i4)}
+
+	return
+}
+
+func textFormatInt(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := args[0].(*tengo.Int)
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.String{Value: strconv.FormatInt(i1.Value, i2)}
+
+	return
+}
+
+func textParseBool(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := args[0].(*tengo.String)
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	parsed, err := strconv.ParseBool(s1.Value)
+	if err != nil {
+		ret = wrapError(err)
+		return
+	}
+
+	if parsed {
+		ret = tengo.TrueValue
+	} else {
+		ret = tengo.FalseValue
+	}
+
+	return
+}
+
+func textParseFloat(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := args[0].(*tengo.String)
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	parsed, err := strconv.ParseFloat(s1.Value, i2)
+	if err != nil {
+		ret = wrapError(err)
+		return
+	}
+
+	ret = &tengo.Float{Value: parsed}
+
+	return
+}
+
+func textParseInt(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 3 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := args[0].(*tengo.String)
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	i3, ok := tengo.ToInt(args[2])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "third",
+			Expected: "int(compatible)",
+			Found:    args[2].TypeName(),
+		}
+		return
+	}
+
+	parsed, err := strconv.ParseInt(s1.Value, i2, i3)
+	if err != nil {
+		ret = wrapError(err)
+		return
+	}
+
+	ret = &tengo.Int{Value: parsed}
+
+	return
+}
+
+// Modified implementation of strings.Replace
+// to limit the maximum length of output string.
+func doTextReplace(s, old, new string, n int) (string, bool) {
+	if old == new || n == 0 {
+		return s, true // avoid allocation
+	}
+
+	// Compute number of replacements.
+	if m := strings.Count(s, old); m == 0 {
+		return s, true // avoid allocation
+	} else if n < 0 || m < n {
+		n = m
+	}
+
+	// Apply replacements to buffer.
+	t := make([]byte, len(s)+n*(len(new)-len(old)))
+	w := 0
+	start := 0
+	for i := 0; i < n; i++ {
+		j := start
+		if len(old) == 0 {
+			if i > 0 {
+				_, wid := utf8.DecodeRuneInString(s[start:])
+				j += wid
+			}
+		} else {
+			j += strings.Index(s[start:], old)
+		}
+
+		ssj := s[start:j]
+		if w+len(ssj)+len(new) > tengo.MaxStringLen {
+			return "", false
+		}
+
+		w += copy(t[w:], ssj)
+		w += copy(t[w:], new)
+		start = j + len(old)
+	}
+
+	ss := s[start:]
+	if w+len(ss) > tengo.MaxStringLen {
+		return "", false
+	}
+
+	w += copy(t[w:], ss)
+
+	return string(t[0:w]), true
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/text_regexp.go b/vendor/github.com/d5/tengo/v2/stdlib/text_regexp.go
new file mode 100644
index 00000000..1a7ecf07
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/text_regexp.go
@@ -0,0 +1,251 @@
+package stdlib
+
+import (
+	"regexp"
+
+	"github.com/d5/tengo/v2"
+)
+
+func makeTextRegexp(re *regexp.Regexp) *tengo.ImmutableMap {
+	return &tengo.ImmutableMap{
+		Value: map[string]tengo.Object{
+			// match(text) => bool
+			"match": &tengo.UserFunction{
+				Value: func(args ...tengo.Object) (
+					ret tengo.Object,
+					err error,
+				) {
+					if len(args) != 1 {
+						err = tengo.ErrWrongNumArguments
+						return
+					}
+
+					s1, ok := tengo.ToString(args[0])
+					if !ok {
+						err = tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "string(compatible)",
+							Found:    args[0].TypeName(),
+						}
+						return
+					}
+
+					if re.MatchString(s1) {
+						ret = tengo.TrueValue
+					} else {
+						ret = tengo.FalseValue
+					}
+
+					return
+				},
+			},
+
+			// find(text) 			=> array(array({text:,begin:,end:}))/undefined
+			// find(text, maxCount) => array(array({text:,begin:,end:}))/undefined
+			"find": &tengo.UserFunction{
+				Value: func(args ...tengo.Object) (
+					ret tengo.Object,
+					err error,
+				) {
+					numArgs := len(args)
+					if numArgs != 1 && numArgs != 2 {
+						err = tengo.ErrWrongNumArguments
+						return
+					}
+
+					s1, ok := tengo.ToString(args[0])
+					if !ok {
+						err = tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "string(compatible)",
+							Found:    args[0].TypeName(),
+						}
+						return
+					}
+
+					if numArgs == 1 {
+						m := re.FindStringSubmatchIndex(s1)
+						if m == nil {
+							ret = tengo.UndefinedValue
+							return
+						}
+
+						arr := &tengo.Array{}
+						for i := 0; i < len(m); i += 2 {
+							arr.Value = append(arr.Value,
+								&tengo.ImmutableMap{
+									Value: map[string]tengo.Object{
+										"text": &tengo.String{
+											Value: s1[m[i]:m[i+1]],
+										},
+										"begin": &tengo.Int{
+											Value: int64(m[i]),
+										},
+										"end": &tengo.Int{
+											Value: int64(m[i+1]),
+										},
+									}})
+						}
+
+						ret = &tengo.Array{Value: []tengo.Object{arr}}
+
+						return
+					}
+
+					i2, ok := tengo.ToInt(args[1])
+					if !ok {
+						err = tengo.ErrInvalidArgumentType{
+							Name:     "second",
+							Expected: "int(compatible)",
+							Found:    args[1].TypeName(),
+						}
+						return
+					}
+					m := re.FindAllStringSubmatchIndex(s1, i2)
+					if m == nil {
+						ret = tengo.UndefinedValue
+						return
+					}
+
+					arr := &tengo.Array{}
+					for _, m := range m {
+						subMatch := &tengo.Array{}
+						for i := 0; i < len(m); i += 2 {
+							subMatch.Value = append(subMatch.Value,
+								&tengo.ImmutableMap{
+									Value: map[string]tengo.Object{
+										"text": &tengo.String{
+											Value: s1[m[i]:m[i+1]],
+										},
+										"begin": &tengo.Int{
+											Value: int64(m[i]),
+										},
+										"end": &tengo.Int{
+											Value: int64(m[i+1]),
+										},
+									}})
+						}
+
+						arr.Value = append(arr.Value, subMatch)
+					}
+
+					ret = arr
+
+					return
+				},
+			},
+
+			// replace(src, repl) => string
+			"replace": &tengo.UserFunction{
+				Value: func(args ...tengo.Object) (
+					ret tengo.Object,
+					err error,
+				) {
+					if len(args) != 2 {
+						err = tengo.ErrWrongNumArguments
+						return
+					}
+
+					s1, ok := tengo.ToString(args[0])
+					if !ok {
+						err = tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "string(compatible)",
+							Found:    args[0].TypeName(),
+						}
+						return
+					}
+
+					s2, ok := tengo.ToString(args[1])
+					if !ok {
+						err = tengo.ErrInvalidArgumentType{
+							Name:     "second",
+							Expected: "string(compatible)",
+							Found:    args[1].TypeName(),
+						}
+						return
+					}
+
+					s, ok := doTextRegexpReplace(re, s1, s2)
+					if !ok {
+						return nil, tengo.ErrStringLimit
+					}
+
+					ret = &tengo.String{Value: s}
+
+					return
+				},
+			},
+
+			// split(text) 			 => array(string)
+			// split(text, maxCount) => array(string)
+			"split": &tengo.UserFunction{
+				Value: func(args ...tengo.Object) (
+					ret tengo.Object,
+					err error,
+				) {
+					numArgs := len(args)
+					if numArgs != 1 && numArgs != 2 {
+						err = tengo.ErrWrongNumArguments
+						return
+					}
+
+					s1, ok := tengo.ToString(args[0])
+					if !ok {
+						err = tengo.ErrInvalidArgumentType{
+							Name:     "first",
+							Expected: "string(compatible)",
+							Found:    args[0].TypeName(),
+						}
+						return
+					}
+
+					var i2 = -1
+					if numArgs > 1 {
+						i2, ok = tengo.ToInt(args[1])
+						if !ok {
+							err = tengo.ErrInvalidArgumentType{
+								Name:     "second",
+								Expected: "int(compatible)",
+								Found:    args[1].TypeName(),
+							}
+							return
+						}
+					}
+
+					arr := &tengo.Array{}
+					for _, s := range re.Split(s1, i2) {
+						arr.Value = append(arr.Value,
+							&tengo.String{Value: s})
+					}
+
+					ret = arr
+
+					return
+				},
+			},
+		},
+	}
+}
+
+// Size-limit checking implementation of regexp.ReplaceAllString.
+func doTextRegexpReplace(re *regexp.Regexp, src, repl string) (string, bool) {
+	idx := 0
+	out := ""
+	for _, m := range re.FindAllStringSubmatchIndex(src, -1) {
+		var exp []byte
+		exp = re.ExpandString(exp, repl, src, m)
+		if len(out)+m[0]-idx+len(exp) > tengo.MaxStringLen {
+			return "", false
+		}
+		out += src[idx:m[0]] + string(exp)
+		idx = m[1]
+	}
+	if idx < len(src) {
+		if len(out)+len(src)-idx > tengo.MaxStringLen {
+			return "", false
+		}
+		out += src[idx:]
+	}
+	return out, true
+}
diff --git a/vendor/github.com/d5/tengo/v2/stdlib/times.go b/vendor/github.com/d5/tengo/v2/stdlib/times.go
new file mode 100644
index 00000000..0b6f7bd4
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/stdlib/times.go
@@ -0,0 +1,1135 @@
+package stdlib
+
+import (
+	"time"
+
+	"github.com/d5/tengo/v2"
+)
+
+var timesModule = map[string]tengo.Object{
+	"format_ansic":        &tengo.String{Value: time.ANSIC},
+	"format_unix_date":    &tengo.String{Value: time.UnixDate},
+	"format_ruby_date":    &tengo.String{Value: time.RubyDate},
+	"format_rfc822":       &tengo.String{Value: time.RFC822},
+	"format_rfc822z":      &tengo.String{Value: time.RFC822Z},
+	"format_rfc850":       &tengo.String{Value: time.RFC850},
+	"format_rfc1123":      &tengo.String{Value: time.RFC1123},
+	"format_rfc1123z":     &tengo.String{Value: time.RFC1123Z},
+	"format_rfc3339":      &tengo.String{Value: time.RFC3339},
+	"format_rfc3339_nano": &tengo.String{Value: time.RFC3339Nano},
+	"format_kitchen":      &tengo.String{Value: time.Kitchen},
+	"format_stamp":        &tengo.String{Value: time.Stamp},
+	"format_stamp_milli":  &tengo.String{Value: time.StampMilli},
+	"format_stamp_micro":  &tengo.String{Value: time.StampMicro},
+	"format_stamp_nano":   &tengo.String{Value: time.StampNano},
+	"nanosecond":          &tengo.Int{Value: int64(time.Nanosecond)},
+	"microsecond":         &tengo.Int{Value: int64(time.Microsecond)},
+	"millisecond":         &tengo.Int{Value: int64(time.Millisecond)},
+	"second":              &tengo.Int{Value: int64(time.Second)},
+	"minute":              &tengo.Int{Value: int64(time.Minute)},
+	"hour":                &tengo.Int{Value: int64(time.Hour)},
+	"january":             &tengo.Int{Value: int64(time.January)},
+	"february":            &tengo.Int{Value: int64(time.February)},
+	"march":               &tengo.Int{Value: int64(time.March)},
+	"april":               &tengo.Int{Value: int64(time.April)},
+	"may":                 &tengo.Int{Value: int64(time.May)},
+	"june":                &tengo.Int{Value: int64(time.June)},
+	"july":                &tengo.Int{Value: int64(time.July)},
+	"august":              &tengo.Int{Value: int64(time.August)},
+	"september":           &tengo.Int{Value: int64(time.September)},
+	"october":             &tengo.Int{Value: int64(time.October)},
+	"november":            &tengo.Int{Value: int64(time.November)},
+	"december":            &tengo.Int{Value: int64(time.December)},
+	"sleep": &tengo.UserFunction{
+		Name:  "sleep",
+		Value: timesSleep,
+	}, // sleep(int)
+	"parse_duration": &tengo.UserFunction{
+		Name:  "parse_duration",
+		Value: timesParseDuration,
+	}, // parse_duration(str) => int
+	"since": &tengo.UserFunction{
+		Name:  "since",
+		Value: timesSince,
+	}, // since(time) => int
+	"until": &tengo.UserFunction{
+		Name:  "until",
+		Value: timesUntil,
+	}, // until(time) => int
+	"duration_hours": &tengo.UserFunction{
+		Name:  "duration_hours",
+		Value: timesDurationHours,
+	}, // duration_hours(int) => float
+	"duration_minutes": &tengo.UserFunction{
+		Name:  "duration_minutes",
+		Value: timesDurationMinutes,
+	}, // duration_minutes(int) => float
+	"duration_nanoseconds": &tengo.UserFunction{
+		Name:  "duration_nanoseconds",
+		Value: timesDurationNanoseconds,
+	}, // duration_nanoseconds(int) => int
+	"duration_seconds": &tengo.UserFunction{
+		Name:  "duration_seconds",
+		Value: timesDurationSeconds,
+	}, // duration_seconds(int) => float
+	"duration_string": &tengo.UserFunction{
+		Name:  "duration_string",
+		Value: timesDurationString,
+	}, // duration_string(int) => string
+	"month_string": &tengo.UserFunction{
+		Name:  "month_string",
+		Value: timesMonthString,
+	}, // month_string(int) => string
+	"date": &tengo.UserFunction{
+		Name:  "date",
+		Value: timesDate,
+	}, // date(year, month, day, hour, min, sec, nsec) => time
+	"now": &tengo.UserFunction{
+		Name:  "now",
+		Value: timesNow,
+	}, // now() => time
+	"parse": &tengo.UserFunction{
+		Name:  "parse",
+		Value: timesParse,
+	}, // parse(format, str) => time
+	"unix": &tengo.UserFunction{
+		Name:  "unix",
+		Value: timesUnix,
+	}, // unix(sec, nsec) => time
+	"add": &tengo.UserFunction{
+		Name:  "add",
+		Value: timesAdd,
+	}, // add(time, int) => time
+	"add_date": &tengo.UserFunction{
+		Name:  "add_date",
+		Value: timesAddDate,
+	}, // add_date(time, years, months, days) => time
+	"sub": &tengo.UserFunction{
+		Name:  "sub",
+		Value: timesSub,
+	}, // sub(t time, u time) => int
+	"after": &tengo.UserFunction{
+		Name:  "after",
+		Value: timesAfter,
+	}, // after(t time, u time) => bool
+	"before": &tengo.UserFunction{
+		Name:  "before",
+		Value: timesBefore,
+	}, // before(t time, u time) => bool
+	"time_year": &tengo.UserFunction{
+		Name:  "time_year",
+		Value: timesTimeYear,
+	}, // time_year(time) => int
+	"time_month": &tengo.UserFunction{
+		Name:  "time_month",
+		Value: timesTimeMonth,
+	}, // time_month(time) => int
+	"time_day": &tengo.UserFunction{
+		Name:  "time_day",
+		Value: timesTimeDay,
+	}, // time_day(time) => int
+	"time_weekday": &tengo.UserFunction{
+		Name:  "time_weekday",
+		Value: timesTimeWeekday,
+	}, // time_weekday(time) => int
+	"time_hour": &tengo.UserFunction{
+		Name:  "time_hour",
+		Value: timesTimeHour,
+	}, // time_hour(time) => int
+	"time_minute": &tengo.UserFunction{
+		Name:  "time_minute",
+		Value: timesTimeMinute,
+	}, // time_minute(time) => int
+	"time_second": &tengo.UserFunction{
+		Name:  "time_second",
+		Value: timesTimeSecond,
+	}, // time_second(time) => int
+	"time_nanosecond": &tengo.UserFunction{
+		Name:  "time_nanosecond",
+		Value: timesTimeNanosecond,
+	}, // time_nanosecond(time) => int
+	"time_unix": &tengo.UserFunction{
+		Name:  "time_unix",
+		Value: timesTimeUnix,
+	}, // time_unix(time) => int
+	"time_unix_nano": &tengo.UserFunction{
+		Name:  "time_unix_nano",
+		Value: timesTimeUnixNano,
+	}, // time_unix_nano(time) => int
+	"time_format": &tengo.UserFunction{
+		Name:  "time_format",
+		Value: timesTimeFormat,
+	}, // time_format(time, format) => string
+	"time_location": &tengo.UserFunction{
+		Name:  "time_location",
+		Value: timesTimeLocation,
+	}, // time_location(time) => string
+	"time_string": &tengo.UserFunction{
+		Name:  "time_string",
+		Value: timesTimeString,
+	}, // time_string(time) => string
+	"is_zero": &tengo.UserFunction{
+		Name:  "is_zero",
+		Value: timesIsZero,
+	}, // is_zero(time) => bool
+	"to_local": &tengo.UserFunction{
+		Name:  "to_local",
+		Value: timesToLocal,
+	}, // to_local(time) => time
+	"to_utc": &tengo.UserFunction{
+		Name:  "to_utc",
+		Value: timesToUTC,
+	}, // to_utc(time) => time
+}
+
+func timesSleep(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := tengo.ToInt64(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	time.Sleep(time.Duration(i1))
+	ret = tengo.UndefinedValue
+
+	return
+}
+
+func timesParseDuration(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	dur, err := time.ParseDuration(s1)
+	if err != nil {
+		ret = wrapError(err)
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(dur)}
+
+	return
+}
+
+func timesSince(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(time.Since(t1))}
+
+	return
+}
+
+func timesUntil(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(time.Until(t1))}
+
+	return
+}
+
+func timesDurationHours(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := tengo.ToInt64(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Float{Value: time.Duration(i1).Hours()}
+
+	return
+}
+
+func timesDurationMinutes(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := tengo.ToInt64(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Float{Value: time.Duration(i1).Minutes()}
+
+	return
+}
+
+func timesDurationNanoseconds(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := tengo.ToInt64(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: time.Duration(i1).Nanoseconds()}
+
+	return
+}
+
+func timesDurationSeconds(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := tengo.ToInt64(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Float{Value: time.Duration(i1).Seconds()}
+
+	return
+}
+
+func timesDurationString(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := tengo.ToInt64(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.String{Value: time.Duration(i1).String()}
+
+	return
+}
+
+func timesMonthString(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := tengo.ToInt64(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.String{Value: time.Month(i1).String()}
+
+	return
+}
+
+func timesDate(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 7 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := tengo.ToInt(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+	i3, ok := tengo.ToInt(args[2])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "third",
+			Expected: "int(compatible)",
+			Found:    args[2].TypeName(),
+		}
+		return
+	}
+	i4, ok := tengo.ToInt(args[3])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "fourth",
+			Expected: "int(compatible)",
+			Found:    args[3].TypeName(),
+		}
+		return
+	}
+	i5, ok := tengo.ToInt(args[4])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "fifth",
+			Expected: "int(compatible)",
+			Found:    args[4].TypeName(),
+		}
+		return
+	}
+	i6, ok := tengo.ToInt(args[5])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "sixth",
+			Expected: "int(compatible)",
+			Found:    args[5].TypeName(),
+		}
+		return
+	}
+	i7, ok := tengo.ToInt(args[6])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "seventh",
+			Expected: "int(compatible)",
+			Found:    args[6].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Time{
+		Value: time.Date(i1,
+			time.Month(i2), i3, i4, i5, i6, i7, time.Now().Location()),
+	}
+
+	return
+}
+
+func timesNow(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 0 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	ret = &tengo.Time{Value: time.Now()}
+
+	return
+}
+
+func timesParse(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	s1, ok := tengo.ToString(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "string(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	s2, ok := tengo.ToString(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	parsed, err := time.Parse(s1, s2)
+	if err != nil {
+		ret = wrapError(err)
+		return
+	}
+
+	ret = &tengo.Time{Value: parsed}
+
+	return
+}
+
+func timesUnix(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	i1, ok := tengo.ToInt64(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "int(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	i2, ok := tengo.ToInt64(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Time{Value: time.Unix(i1, i2)}
+
+	return
+}
+
+func timesAdd(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	i2, ok := tengo.ToInt64(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Time{Value: t1.Add(time.Duration(i2))}
+
+	return
+}
+
+func timesSub(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	t2, ok := tengo.ToTime(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "time(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(t1.Sub(t2))}
+
+	return
+}
+
+func timesAddDate(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 4 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	i2, ok := tengo.ToInt(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "int(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	i3, ok := tengo.ToInt(args[2])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "third",
+			Expected: "int(compatible)",
+			Found:    args[2].TypeName(),
+		}
+		return
+	}
+
+	i4, ok := tengo.ToInt(args[3])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "fourth",
+			Expected: "int(compatible)",
+			Found:    args[3].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Time{Value: t1.AddDate(i2, i3, i4)}
+
+	return
+}
+
+func timesAfter(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	t2, ok := tengo.ToTime(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "time(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	if t1.After(t2) {
+		ret = tengo.TrueValue
+	} else {
+		ret = tengo.FalseValue
+	}
+
+	return
+}
+
+func timesBefore(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	t2, ok := tengo.ToTime(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	if t1.Before(t2) {
+		ret = tengo.TrueValue
+	} else {
+		ret = tengo.FalseValue
+	}
+
+	return
+}
+
+func timesTimeYear(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(t1.Year())}
+
+	return
+}
+
+func timesTimeMonth(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(t1.Month())}
+
+	return
+}
+
+func timesTimeDay(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(t1.Day())}
+
+	return
+}
+
+func timesTimeWeekday(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(t1.Weekday())}
+
+	return
+}
+
+func timesTimeHour(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(t1.Hour())}
+
+	return
+}
+
+func timesTimeMinute(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(t1.Minute())}
+
+	return
+}
+
+func timesTimeSecond(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(t1.Second())}
+
+	return
+}
+
+func timesTimeNanosecond(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: int64(t1.Nanosecond())}
+
+	return
+}
+
+func timesTimeUnix(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: t1.Unix()}
+
+	return
+}
+
+func timesTimeUnixNano(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Int{Value: t1.UnixNano()}
+
+	return
+}
+
+func timesTimeFormat(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 2 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	s2, ok := tengo.ToString(args[1])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "second",
+			Expected: "string(compatible)",
+			Found:    args[1].TypeName(),
+		}
+		return
+	}
+
+	s := t1.Format(s2)
+	if len(s) > tengo.MaxStringLen {
+
+		return nil, tengo.ErrStringLimit
+	}
+
+	ret = &tengo.String{Value: s}
+
+	return
+}
+
+func timesIsZero(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	if t1.IsZero() {
+		ret = tengo.TrueValue
+	} else {
+		ret = tengo.FalseValue
+	}
+
+	return
+}
+
+func timesToLocal(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Time{Value: t1.Local()}
+
+	return
+}
+
+func timesToUTC(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.Time{Value: t1.UTC()}
+
+	return
+}
+
+func timesTimeLocation(args ...tengo.Object) (
+	ret tengo.Object,
+	err error,
+) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.String{Value: t1.Location().String()}
+
+	return
+}
+
+func timesTimeString(args ...tengo.Object) (ret tengo.Object, err error) {
+	if len(args) != 1 {
+		err = tengo.ErrWrongNumArguments
+		return
+	}
+
+	t1, ok := tengo.ToTime(args[0])
+	if !ok {
+		err = tengo.ErrInvalidArgumentType{
+			Name:     "first",
+			Expected: "time(compatible)",
+			Found:    args[0].TypeName(),
+		}
+		return
+	}
+
+	ret = &tengo.String{Value: t1.String()}
+
+	return
+}
diff --git a/vendor/github.com/d5/tengo/v2/symbol_table.go b/vendor/github.com/d5/tengo/v2/symbol_table.go
new file mode 100644
index 00000000..6ae5d7d3
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/symbol_table.go
@@ -0,0 +1,165 @@
+package tengo
+
+// SymbolScope represents a symbol scope.
+type SymbolScope string
+
+// List of symbol scopes
+const (
+	ScopeGlobal  SymbolScope = "GLOBAL"
+	ScopeLocal   SymbolScope = "LOCAL"
+	ScopeBuiltin SymbolScope = "BUILTIN"
+	ScopeFree    SymbolScope = "FREE"
+)
+
+// Symbol represents a symbol in the symbol table.
+type Symbol struct {
+	Name          string
+	Scope         SymbolScope
+	Index         int
+	LocalAssigned bool // if the local symbol is assigned at least once
+}
+
+// SymbolTable represents a symbol table.
+type SymbolTable struct {
+	parent         *SymbolTable
+	block          bool
+	store          map[string]*Symbol
+	numDefinition  int
+	maxDefinition  int
+	freeSymbols    []*Symbol
+	builtinSymbols []*Symbol
+}
+
+// NewSymbolTable creates a SymbolTable.
+func NewSymbolTable() *SymbolTable {
+	return &SymbolTable{
+		store: make(map[string]*Symbol),
+	}
+}
+
+// Define adds a new symbol in the current scope.
+func (t *SymbolTable) Define(name string) *Symbol {
+	symbol := &Symbol{Name: name, Index: t.nextIndex()}
+	t.numDefinition++
+
+	if t.Parent(true) == nil {
+		symbol.Scope = ScopeGlobal
+	} else {
+		symbol.Scope = ScopeLocal
+	}
+	t.store[name] = symbol
+	t.updateMaxDefs(symbol.Index + 1)
+	return symbol
+}
+
+// DefineBuiltin adds a symbol for builtin function.
+func (t *SymbolTable) DefineBuiltin(index int, name string) *Symbol {
+	if t.parent != nil {
+		return t.parent.DefineBuiltin(index, name)
+	}
+
+	symbol := &Symbol{
+		Name:  name,
+		Index: index,
+		Scope: ScopeBuiltin,
+	}
+	t.store[name] = symbol
+	t.builtinSymbols = append(t.builtinSymbols, symbol)
+	return symbol
+}
+
+// Resolve resolves a symbol with a given name.
+func (t *SymbolTable) Resolve(
+	name string,
+) (symbol *Symbol, depth int, ok bool) {
+	symbol, ok = t.store[name]
+	if !ok && t.parent != nil {
+		symbol, depth, ok = t.parent.Resolve(name)
+		if !ok {
+			return
+		}
+		depth++
+
+		// if symbol is defined in parent table and if it's not global/builtin
+		// then it's free variable.
+		if !t.block && depth > 0 &&
+			symbol.Scope != ScopeGlobal &&
+			symbol.Scope != ScopeBuiltin {
+			return t.defineFree(symbol), depth, true
+		}
+		return
+	}
+	return
+}
+
+// Fork creates a new symbol table for a new scope.
+func (t *SymbolTable) Fork(block bool) *SymbolTable {
+	return &SymbolTable{
+		store:  make(map[string]*Symbol),
+		parent: t,
+		block:  block,
+	}
+}
+
+// Parent returns the outer scope of the current symbol table.
+func (t *SymbolTable) Parent(skipBlock bool) *SymbolTable {
+	if skipBlock && t.block {
+		return t.parent.Parent(skipBlock)
+	}
+	return t.parent
+}
+
+// MaxSymbols returns the total number of symbols defined in the scope.
+func (t *SymbolTable) MaxSymbols() int {
+	return t.maxDefinition
+}
+
+// FreeSymbols returns free symbols for the scope.
+func (t *SymbolTable) FreeSymbols() []*Symbol {
+	return t.freeSymbols
+}
+
+// BuiltinSymbols returns builtin symbols for the scope.
+func (t *SymbolTable) BuiltinSymbols() []*Symbol {
+	if t.parent != nil {
+		return t.parent.BuiltinSymbols()
+	}
+	return t.builtinSymbols
+}
+
+// Names returns the name of all the symbols.
+func (t *SymbolTable) Names() []string {
+	var names []string
+	for name := range t.store {
+		names = append(names, name)
+	}
+	return names
+}
+
+func (t *SymbolTable) nextIndex() int {
+	if t.block {
+		return t.parent.nextIndex() + t.numDefinition
+	}
+	return t.numDefinition
+}
+
+func (t *SymbolTable) updateMaxDefs(numDefs int) {
+	if numDefs > t.maxDefinition {
+		t.maxDefinition = numDefs
+	}
+	if t.block {
+		t.parent.updateMaxDefs(numDefs)
+	}
+}
+
+func (t *SymbolTable) defineFree(original *Symbol) *Symbol {
+	// TODO: should we check duplicates?
+	t.freeSymbols = append(t.freeSymbols, original)
+	symbol := &Symbol{
+		Name:  original.Name,
+		Index: len(t.freeSymbols) - 1,
+		Scope: ScopeFree,
+	}
+	t.store[original.Name] = symbol
+	return symbol
+}
diff --git a/vendor/github.com/d5/tengo/v2/tengo.go b/vendor/github.com/d5/tengo/v2/tengo.go
new file mode 100644
index 00000000..098a1970
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/tengo.go
@@ -0,0 +1,306 @@
+package tengo
+
+import (
+	"errors"
+	"fmt"
+	"strconv"
+	"time"
+)
+
+var (
+	// MaxStringLen is the maximum byte-length for string value. Note this
+	// limit applies to all compiler/VM instances in the process.
+	MaxStringLen = 2147483647
+
+	// MaxBytesLen is the maximum length for bytes value. Note this limit
+	// applies to all compiler/VM instances in the process.
+	MaxBytesLen = 2147483647
+)
+
+const (
+	// GlobalsSize is the maximum number of global variables for a VM.
+	GlobalsSize = 1024
+
+	// StackSize is the maximum stack size for a VM.
+	StackSize = 2048
+
+	// MaxFrames is the maximum number of function frames for a VM.
+	MaxFrames = 1024
+)
+
+// CallableFunc is a function signature for the callable functions.
+type CallableFunc = func(args ...Object) (ret Object, err error)
+
+// CountObjects returns the number of objects that a given object o contains.
+// For scalar value types, it will always be 1. For compound value types,
+// this will include its elements and all of their elements recursively.
+func CountObjects(o Object) (c int) {
+	c = 1
+	switch o := o.(type) {
+	case *Array:
+		for _, v := range o.Value {
+			c += CountObjects(v)
+		}
+	case *ImmutableArray:
+		for _, v := range o.Value {
+			c += CountObjects(v)
+		}
+	case *Map:
+		for _, v := range o.Value {
+			c += CountObjects(v)
+		}
+	case *ImmutableMap:
+		for _, v := range o.Value {
+			c += CountObjects(v)
+		}
+	case *Error:
+		c += CountObjects(o.Value)
+	}
+	return
+}
+
+// ToString will try to convert object o to string value.
+func ToString(o Object) (v string, ok bool) {
+	if o == UndefinedValue {
+		return
+	}
+	ok = true
+	if str, isStr := o.(*String); isStr {
+		v = str.Value
+	} else {
+		v = o.String()
+	}
+	return
+}
+
+// ToInt will try to convert object o to int value.
+func ToInt(o Object) (v int, ok bool) {
+	switch o := o.(type) {
+	case *Int:
+		v = int(o.Value)
+		ok = true
+	case *Float:
+		v = int(o.Value)
+		ok = true
+	case *Char:
+		v = int(o.Value)
+		ok = true
+	case *Bool:
+		if o == TrueValue {
+			v = 1
+		}
+		ok = true
+	case *String:
+		c, err := strconv.ParseInt(o.Value, 10, 64)
+		if err == nil {
+			v = int(c)
+			ok = true
+		}
+	}
+	return
+}
+
+// ToInt64 will try to convert object o to int64 value.
+func ToInt64(o Object) (v int64, ok bool) {
+	switch o := o.(type) {
+	case *Int:
+		v = o.Value
+		ok = true
+	case *Float:
+		v = int64(o.Value)
+		ok = true
+	case *Char:
+		v = int64(o.Value)
+		ok = true
+	case *Bool:
+		if o == TrueValue {
+			v = 1
+		}
+		ok = true
+	case *String:
+		c, err := strconv.ParseInt(o.Value, 10, 64)
+		if err == nil {
+			v = c
+			ok = true
+		}
+	}
+	return
+}
+
+// ToFloat64 will try to convert object o to float64 value.
+func ToFloat64(o Object) (v float64, ok bool) {
+	switch o := o.(type) {
+	case *Int:
+		v = float64(o.Value)
+		ok = true
+	case *Float:
+		v = o.Value
+		ok = true
+	case *String:
+		c, err := strconv.ParseFloat(o.Value, 64)
+		if err == nil {
+			v = c
+			ok = true
+		}
+	}
+	return
+}
+
+// ToBool will try to convert object o to bool value.
+func ToBool(o Object) (v bool, ok bool) {
+	ok = true
+	v = !o.IsFalsy()
+	return
+}
+
+// ToRune will try to convert object o to rune value.
+func ToRune(o Object) (v rune, ok bool) {
+	switch o := o.(type) {
+	case *Int:
+		v = rune(o.Value)
+		ok = true
+	case *Char:
+		v = o.Value
+		ok = true
+	}
+	return
+}
+
+// ToByteSlice will try to convert object o to []byte value.
+func ToByteSlice(o Object) (v []byte, ok bool) {
+	switch o := o.(type) {
+	case *Bytes:
+		v = o.Value
+		ok = true
+	case *String:
+		v = []byte(o.Value)
+		ok = true
+	}
+	return
+}
+
+// ToTime will try to convert object o to time.Time value.
+func ToTime(o Object) (v time.Time, ok bool) {
+	switch o := o.(type) {
+	case *Time:
+		v = o.Value
+		ok = true
+	case *Int:
+		v = time.Unix(o.Value, 0)
+		ok = true
+	}
+	return
+}
+
+// ToInterface attempts to convert an object o to an interface{} value
+func ToInterface(o Object) (res interface{}) {
+	switch o := o.(type) {
+	case *Int:
+		res = o.Value
+	case *String:
+		res = o.Value
+	case *Float:
+		res = o.Value
+	case *Bool:
+		res = o == TrueValue
+	case *Char:
+		res = o.Value
+	case *Bytes:
+		res = o.Value
+	case *Array:
+		res = make([]interface{}, len(o.Value))
+		for i, val := range o.Value {
+			res.([]interface{})[i] = ToInterface(val)
+		}
+	case *ImmutableArray:
+		res = make([]interface{}, len(o.Value))
+		for i, val := range o.Value {
+			res.([]interface{})[i] = ToInterface(val)
+		}
+	case *Map:
+		res = make(map[string]interface{})
+		for key, v := range o.Value {
+			res.(map[string]interface{})[key] = ToInterface(v)
+		}
+	case *ImmutableMap:
+		res = make(map[string]interface{})
+		for key, v := range o.Value {
+			res.(map[string]interface{})[key] = ToInterface(v)
+		}
+	case *Time:
+		res = o.Value
+	case *Error:
+		res = errors.New(o.String())
+	case *Undefined:
+		res = nil
+	case Object:
+		return o
+	}
+	return
+}
+
+// FromInterface will attempt to convert an interface{} v to a Tengo Object
+func FromInterface(v interface{}) (Object, error) {
+	switch v := v.(type) {
+	case nil:
+		return UndefinedValue, nil
+	case string:
+		if len(v) > MaxStringLen {
+			return nil, ErrStringLimit
+		}
+		return &String{Value: v}, nil
+	case int64:
+		return &Int{Value: v}, nil
+	case int:
+		return &Int{Value: int64(v)}, nil
+	case bool:
+		if v {
+			return TrueValue, nil
+		}
+		return FalseValue, nil
+	case rune:
+		return &Char{Value: v}, nil
+	case byte:
+		return &Char{Value: rune(v)}, nil
+	case float64:
+		return &Float{Value: v}, nil
+	case []byte:
+		if len(v) > MaxBytesLen {
+			return nil, ErrBytesLimit
+		}
+		return &Bytes{Value: v}, nil
+	case error:
+		return &Error{Value: &String{Value: v.Error()}}, nil
+	case map[string]Object:
+		return &Map{Value: v}, nil
+	case map[string]interface{}:
+		kv := make(map[string]Object)
+		for vk, vv := range v {
+			vo, err := FromInterface(vv)
+			if err != nil {
+				return nil, err
+			}
+			kv[vk] = vo
+		}
+		return &Map{Value: kv}, nil
+	case []Object:
+		return &Array{Value: v}, nil
+	case []interface{}:
+		arr := make([]Object, len(v))
+		for i, e := range v {
+			vo, err := FromInterface(e)
+			if err != nil {
+				return nil, err
+			}
+			arr[i] = vo
+		}
+		return &Array{Value: arr}, nil
+	case time.Time:
+		return &Time{Value: v}, nil
+	case Object:
+		return v, nil
+	case CallableFunc:
+		return &UserFunction{Value: v}, nil
+	}
+	return nil, fmt.Errorf("cannot convert to object: %T", v)
+}
diff --git a/vendor/github.com/d5/tengo/v2/token/token.go b/vendor/github.com/d5/tengo/v2/token/token.go
new file mode 100644
index 00000000..4e6aa80a
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/token/token.go
@@ -0,0 +1,225 @@
+package token
+
+import "strconv"
+
+var keywords map[string]Token
+
+// Token represents a token.
+type Token int
+
+// List of tokens
+const (
+	Illegal Token = iota
+	EOF
+	Comment
+	_literalBeg
+	Ident
+	Int
+	Float
+	Char
+	String
+	_literalEnd
+	_operatorBeg
+	Add          // +
+	Sub          // -
+	Mul          // *
+	Quo          // /
+	Rem          // %
+	And          // &
+	Or           // |
+	Xor          // ^
+	Shl          // <<
+	Shr          // >>
+	AndNot       // &^
+	AddAssign    // +=
+	SubAssign    // -=
+	MulAssign    // *=
+	QuoAssign    // /=
+	RemAssign    // %=
+	AndAssign    // &=
+	OrAssign     // |=
+	XorAssign    // ^=
+	ShlAssign    // <<=
+	ShrAssign    // >>=
+	AndNotAssign // &^=
+	LAnd         // &&
+	LOr          // ||
+	Inc          // ++
+	Dec          // --
+	Equal        // ==
+	Less         // <
+	Greater      // >
+	Assign       // =
+	Not          // !
+	NotEqual     // !=
+	LessEq       // <=
+	GreaterEq    // >=
+	Define       // :=
+	Ellipsis     // ...
+	LParen       // (
+	LBrack       // [
+	LBrace       // {
+	Comma        // ,
+	Period       // .
+	RParen       // )
+	RBrack       // ]
+	RBrace       // }
+	Semicolon    // ;
+	Colon        // :
+	Question     // ?
+	_operatorEnd
+	_keywordBeg
+	Break
+	Continue
+	Else
+	For
+	Func
+	Error
+	Immutable
+	If
+	Return
+	Export
+	True
+	False
+	In
+	Undefined
+	Import
+	_keywordEnd
+)
+
+var tokens = [...]string{
+	Illegal:      "ILLEGAL",
+	EOF:          "EOF",
+	Comment:      "COMMENT",
+	Ident:        "IDENT",
+	Int:          "INT",
+	Float:        "FLOAT",
+	Char:         "CHAR",
+	String:       "STRING",
+	Add:          "+",
+	Sub:          "-",
+	Mul:          "*",
+	Quo:          "/",
+	Rem:          "%",
+	And:          "&",
+	Or:           "|",
+	Xor:          "^",
+	Shl:          "<<",
+	Shr:          ">>",
+	AndNot:       "&^",
+	AddAssign:    "+=",
+	SubAssign:    "-=",
+	MulAssign:    "*=",
+	QuoAssign:    "/=",
+	RemAssign:    "%=",
+	AndAssign:    "&=",
+	OrAssign:     "|=",
+	XorAssign:    "^=",
+	ShlAssign:    "<<=",
+	ShrAssign:    ">>=",
+	AndNotAssign: "&^=",
+	LAnd:         "&&",
+	LOr:          "||",
+	Inc:          "++",
+	Dec:          "--",
+	Equal:        "==",
+	Less:         "<",
+	Greater:      ">",
+	Assign:       "=",
+	Not:          "!",
+	NotEqual:     "!=",
+	LessEq:       "<=",
+	GreaterEq:    ">=",
+	Define:       ":=",
+	Ellipsis:     "...",
+	LParen:       "(",
+	LBrack:       "[",
+	LBrace:       "{",
+	Comma:        ",",
+	Period:       ".",
+	RParen:       ")",
+	RBrack:       "]",
+	RBrace:       "}",
+	Semicolon:    ";",
+	Colon:        ":",
+	Question:     "?",
+	Break:        "break",
+	Continue:     "continue",
+	Else:         "else",
+	For:          "for",
+	Func:         "func",
+	Error:        "error",
+	Immutable:    "immutable",
+	If:           "if",
+	Return:       "return",
+	Export:       "export",
+	True:         "true",
+	False:        "false",
+	In:           "in",
+	Undefined:    "undefined",
+	Import:       "import",
+}
+
+func (tok Token) String() string {
+	s := ""
+
+	if 0 <= tok && tok < Token(len(tokens)) {
+		s = tokens[tok]
+	}
+
+	if s == "" {
+		s = "token(" + strconv.Itoa(int(tok)) + ")"
+	}
+
+	return s
+}
+
+// LowestPrec represents lowest operator precedence.
+const LowestPrec = 0
+
+// Precedence returns the precedence for the operator token.
+func (tok Token) Precedence() int {
+	switch tok {
+	case LOr:
+		return 1
+	case LAnd:
+		return 2
+	case Equal, NotEqual, Less, LessEq, Greater, GreaterEq:
+		return 3
+	case Add, Sub, Or, Xor:
+		return 4
+	case Mul, Quo, Rem, Shl, Shr, And, AndNot:
+		return 5
+	}
+	return LowestPrec
+}
+
+// IsLiteral returns true if the token is a literal.
+func (tok Token) IsLiteral() bool {
+	return _literalBeg < tok && tok < _literalEnd
+}
+
+// IsOperator returns true if the token is an operator.
+func (tok Token) IsOperator() bool {
+	return _operatorBeg < tok && tok < _operatorEnd
+}
+
+// IsKeyword returns true if the token is a keyword.
+func (tok Token) IsKeyword() bool {
+	return _keywordBeg < tok && tok < _keywordEnd
+}
+
+// Lookup returns corresponding keyword if ident is a keyword.
+func Lookup(ident string) Token {
+	if tok, isKeyword := keywords[ident]; isKeyword {
+		return tok
+	}
+	return Ident
+}
+
+func init() {
+	keywords = make(map[string]Token)
+	for i := _keywordBeg + 1; i < _keywordEnd; i++ {
+		keywords[tokens[i]] = i
+	}
+}
diff --git a/vendor/github.com/d5/tengo/v2/variable.go b/vendor/github.com/d5/tengo/v2/variable.go
new file mode 100644
index 00000000..481b36b8
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/variable.go
@@ -0,0 +1,136 @@
+package tengo
+
+import (
+	"errors"
+)
+
+// Variable is a user-defined variable for the script.
+type Variable struct {
+	name  string
+	value Object
+}
+
+// NewVariable creates a Variable.
+func NewVariable(name string, value interface{}) (*Variable, error) {
+	obj, err := FromInterface(value)
+	if err != nil {
+		return nil, err
+	}
+	return &Variable{
+		name:  name,
+		value: obj,
+	}, nil
+}
+
+// Name returns the name of the variable.
+func (v *Variable) Name() string {
+	return v.name
+}
+
+// Value returns an empty interface of the variable value.
+func (v *Variable) Value() interface{} {
+	return ToInterface(v.value)
+}
+
+// ValueType returns the name of the value type.
+func (v *Variable) ValueType() string {
+	return v.value.TypeName()
+}
+
+// Int returns int value of the variable value.
+// It returns 0 if the value is not convertible to int.
+func (v *Variable) Int() int {
+	c, _ := ToInt(v.value)
+	return c
+}
+
+// Int64 returns int64 value of the variable value. It returns 0 if the value
+// is not convertible to int64.
+func (v *Variable) Int64() int64 {
+	c, _ := ToInt64(v.value)
+	return c
+}
+
+// Float returns float64 value of the variable value. It returns 0.0 if the
+// value is not convertible to float64.
+func (v *Variable) Float() float64 {
+	c, _ := ToFloat64(v.value)
+	return c
+}
+
+// Char returns rune value of the variable value. It returns 0 if the value is
+// not convertible to rune.
+func (v *Variable) Char() rune {
+	c, _ := ToRune(v.value)
+	return c
+}
+
+// Bool returns bool value of the variable value. It returns 0 if the value is
+// not convertible to bool.
+func (v *Variable) Bool() bool {
+	c, _ := ToBool(v.value)
+	return c
+}
+
+// Array returns []interface value of the variable value. It returns 0 if the
+// value is not convertible to []interface.
+func (v *Variable) Array() []interface{} {
+	switch val := v.value.(type) {
+	case *Array:
+		var arr []interface{}
+		for _, e := range val.Value {
+			arr = append(arr, ToInterface(e))
+		}
+		return arr
+	}
+	return nil
+}
+
+// Map returns map[string]interface{} value of the variable value. It returns
+// 0 if the value is not convertible to map[string]interface{}.
+func (v *Variable) Map() map[string]interface{} {
+	switch val := v.value.(type) {
+	case *Map:
+		kv := make(map[string]interface{})
+		for mk, mv := range val.Value {
+			kv[mk] = ToInterface(mv)
+		}
+		return kv
+	}
+	return nil
+}
+
+// String returns string value of the variable value. It returns 0 if the value
+// is not convertible to string.
+func (v *Variable) String() string {
+	c, _ := ToString(v.value)
+	return c
+}
+
+// Bytes returns a byte slice of the variable value. It returns nil if the
+// value is not convertible to byte slice.
+func (v *Variable) Bytes() []byte {
+	c, _ := ToByteSlice(v.value)
+	return c
+}
+
+// Error returns an error if the underlying value is error object. If not,
+// this returns nil.
+func (v *Variable) Error() error {
+	err, ok := v.value.(*Error)
+	if ok {
+		return errors.New(err.String())
+	}
+	return nil
+}
+
+// Object returns an underlying Object of the variable value. Note that
+// returned Object is a copy of an actual Object used in the script.
+func (v *Variable) Object() Object {
+	return v.value
+}
+
+// IsUndefined returns true if the underlying value is undefined.
+func (v *Variable) IsUndefined() bool {
+	return v.value == UndefinedValue
+}
diff --git a/vendor/github.com/d5/tengo/v2/vm.go b/vendor/github.com/d5/tengo/v2/vm.go
new file mode 100644
index 00000000..783a54a9
--- /dev/null
+++ b/vendor/github.com/d5/tengo/v2/vm.go
@@ -0,0 +1,883 @@
+package tengo
+
+import (
+	"fmt"
+	"sync/atomic"
+
+	"github.com/d5/tengo/v2/parser"
+	"github.com/d5/tengo/v2/token"
+)
+
+// frame represents a function call frame.
+type frame struct {
+	fn          *CompiledFunction
+	freeVars    []*ObjectPtr
+	ip          int
+	basePointer int
+}
+
+// VM is a virtual machine that executes the bytecode compiled by Compiler.
+type VM struct {
+	constants   []Object
+	stack       [StackSize]Object
+	sp          int
+	globals     []Object
+	fileSet     *parser.SourceFileSet
+	frames      [MaxFrames]frame
+	framesIndex int
+	curFrame    *frame
+	curInsts    []byte
+	ip          int
+	aborting    int64
+	maxAllocs   int64
+	allocs      int64
+	err         error
+}
+
+// NewVM creates a VM.
+func NewVM(
+	bytecode *Bytecode,
+	globals []Object,
+	maxAllocs int64,
+) *VM {
+	if globals == nil {
+		globals = make([]Object, GlobalsSize)
+	}
+	v := &VM{
+		constants:   bytecode.Constants,
+		sp:          0,
+		globals:     globals,
+		fileSet:     bytecode.FileSet,
+		framesIndex: 1,
+		ip:          -1,
+		maxAllocs:   maxAllocs,
+	}
+	v.frames[0].fn = bytecode.MainFunction
+	v.frames[0].ip = -1
+	v.curFrame = &v.frames[0]
+	v.curInsts = v.curFrame.fn.Instructions
+	return v
+}
+
+// Abort aborts the execution.
+func (v *VM) Abort() {
+	atomic.StoreInt64(&v.aborting, 1)
+}
+
+// Run starts the execution.
+func (v *VM) Run() (err error) {
+	// reset VM states
+	v.sp = 0
+	v.curFrame = &(v.frames[0])
+	v.curInsts = v.curFrame.fn.Instructions
+	v.framesIndex = 1
+	v.ip = -1
+	v.allocs = v.maxAllocs + 1
+
+	v.run()
+	atomic.StoreInt64(&v.aborting, 0)
+	err = v.err
+	if err != nil {
+		filePos := v.fileSet.Position(
+			v.curFrame.fn.SourcePos(v.ip - 1))
+		err = fmt.Errorf("Runtime Error: %s\n\tat %s",
+			err.Error(), filePos)
+		for v.framesIndex > 1 {
+			v.framesIndex--
+			v.curFrame = &v.frames[v.framesIndex-1]
+			filePos = v.fileSet.Position(
+				v.curFrame.fn.SourcePos(v.curFrame.ip - 1))
+			err = fmt.Errorf("%s\n\tat %s", err.Error(), filePos)
+		}
+		return err
+	}
+	return nil
+}
+
+func (v *VM) run() {
+	for atomic.LoadInt64(&v.aborting) == 0 {
+		v.ip++
+
+		switch v.curInsts[v.ip] {
+		case parser.OpConstant:
+			v.ip += 2
+			cidx := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
+
+			v.stack[v.sp] = v.constants[cidx]
+			v.sp++
+		case parser.OpNull:
+			v.stack[v.sp] = UndefinedValue
+			v.sp++
+		case parser.OpBinaryOp:
+			v.ip++
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			tok := token.Token(v.curInsts[v.ip])
+			res, e := left.BinaryOp(tok, right)
+			if e != nil {
+				v.sp -= 2
+				if e == ErrInvalidOperator {
+					v.err = fmt.Errorf("invalid operation: %s %s %s",
+						left.TypeName(), tok.String(), right.TypeName())
+					return
+				}
+				v.err = e
+				return
+			}
+
+			v.allocs--
+			if v.allocs == 0 {
+				v.err = ErrObjectAllocLimit
+				return
+			}
+
+			v.stack[v.sp-2] = res
+			v.sp--
+		case parser.OpEqual:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+			if left.Equals(right) {
+				v.stack[v.sp] = TrueValue
+			} else {
+				v.stack[v.sp] = FalseValue
+			}
+			v.sp++
+		case parser.OpNotEqual:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+			if left.Equals(right) {
+				v.stack[v.sp] = FalseValue
+			} else {
+				v.stack[v.sp] = TrueValue
+			}
+			v.sp++
+		case parser.OpPop:
+			v.sp--
+		case parser.OpTrue:
+			v.stack[v.sp] = TrueValue
+			v.sp++
+		case parser.OpFalse:
+			v.stack[v.sp] = FalseValue
+			v.sp++
+		case parser.OpLNot:
+			operand := v.stack[v.sp-1]
+			v.sp--
+			if operand.IsFalsy() {
+				v.stack[v.sp] = TrueValue
+			} else {
+				v.stack[v.sp] = FalseValue
+			}
+			v.sp++
+		case parser.OpBComplement:
+			operand := v.stack[v.sp-1]
+			v.sp--
+
+			switch x := operand.(type) {
+			case *Int:
+				var res Object = &Int{Value: ^x.Value}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp] = res
+				v.sp++
+			default:
+				v.err = fmt.Errorf("invalid operation: ^%s",
+					operand.TypeName())
+				return
+			}
+		case parser.OpMinus:
+			operand := v.stack[v.sp-1]
+			v.sp--
+
+			switch x := operand.(type) {
+			case *Int:
+				var res Object = &Int{Value: -x.Value}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp] = res
+				v.sp++
+			case *Float:
+				var res Object = &Float{Value: -x.Value}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp] = res
+				v.sp++
+			default:
+				v.err = fmt.Errorf("invalid operation: -%s",
+					operand.TypeName())
+				return
+			}
+		case parser.OpJumpFalsy:
+			v.ip += 2
+			v.sp--
+			if v.stack[v.sp].IsFalsy() {
+				pos := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
+				v.ip = pos - 1
+			}
+		case parser.OpAndJump:
+			v.ip += 2
+			if v.stack[v.sp-1].IsFalsy() {
+				pos := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
+				v.ip = pos - 1
+			} else {
+				v.sp--
+			}
+		case parser.OpOrJump:
+			v.ip += 2
+			if v.stack[v.sp-1].IsFalsy() {
+				v.sp--
+			} else {
+				pos := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
+				v.ip = pos - 1
+			}
+		case parser.OpJump:
+			pos := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip = pos - 1
+		case parser.OpSetGlobal:
+			v.ip += 2
+			v.sp--
+			globalIndex := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
+			v.globals[globalIndex] = v.stack[v.sp]
+		case parser.OpSetSelGlobal:
+			v.ip += 3
+			globalIndex := int(v.curInsts[v.ip-1]) | int(v.curInsts[v.ip-2])<<8
+			numSelectors := int(v.curInsts[v.ip])
+
+			// selectors and RHS value
+			selectors := make([]Object, numSelectors)
+			for i := 0; i < numSelectors; i++ {
+				selectors[i] = v.stack[v.sp-numSelectors+i]
+			}
+			val := v.stack[v.sp-numSelectors-1]
+			v.sp -= numSelectors + 1
+			e := indexAssign(v.globals[globalIndex], val, selectors)
+			if e != nil {
+				v.err = e
+				return
+			}
+		case parser.OpGetGlobal:
+			v.ip += 2
+			globalIndex := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
+			val := v.globals[globalIndex]
+			v.stack[v.sp] = val
+			v.sp++
+		case parser.OpArray:
+			v.ip += 2
+			numElements := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
+
+			var elements []Object
+			for i := v.sp - numElements; i < v.sp; i++ {
+				elements = append(elements, v.stack[i])
+			}
+			v.sp -= numElements
+
+			var arr Object = &Array{Value: elements}
+			v.allocs--
+			if v.allocs == 0 {
+				v.err = ErrObjectAllocLimit
+				return
+			}
+
+			v.stack[v.sp] = arr
+			v.sp++
+		case parser.OpMap:
+			v.ip += 2
+			numElements := int(v.curInsts[v.ip]) | int(v.curInsts[v.ip-1])<<8
+			kv := make(map[string]Object)
+			for i := v.sp - numElements; i < v.sp; i += 2 {
+				key := v.stack[i]
+				value := v.stack[i+1]
+				kv[key.(*String).Value] = value
+			}
+			v.sp -= numElements
+
+			var m Object = &Map{Value: kv}
+			v.allocs--
+			if v.allocs == 0 {
+				v.err = ErrObjectAllocLimit
+				return
+			}
+			v.stack[v.sp] = m
+			v.sp++
+		case parser.OpError:
+			value := v.stack[v.sp-1]
+			var e Object = &Error{
+				Value: value,
+			}
+			v.allocs--
+			if v.allocs == 0 {
+				v.err = ErrObjectAllocLimit
+				return
+			}
+			v.stack[v.sp-1] = e
+		case parser.OpImmutable:
+			value := v.stack[v.sp-1]
+			switch value := value.(type) {
+			case *Array:
+				var immutableArray Object = &ImmutableArray{
+					Value: value.Value,
+				}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp-1] = immutableArray
+			case *Map:
+				var immutableMap Object = &ImmutableMap{
+					Value: value.Value,
+				}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp-1] = immutableMap
+			}
+		case parser.OpIndex:
+			index := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			val, err := left.IndexGet(index)
+			if err != nil {
+				if err == ErrNotIndexable {
+					v.err = fmt.Errorf("not indexable: %s", index.TypeName())
+					return
+				}
+				if err == ErrInvalidIndexType {
+					v.err = fmt.Errorf("invalid index type: %s",
+						index.TypeName())
+					return
+				}
+				v.err = err
+				return
+			}
+			if val == nil {
+				val = UndefinedValue
+			}
+			v.stack[v.sp] = val
+			v.sp++
+		case parser.OpSliceIndex:
+			high := v.stack[v.sp-1]
+			low := v.stack[v.sp-2]
+			left := v.stack[v.sp-3]
+			v.sp -= 3
+
+			var lowIdx int64
+			if low != UndefinedValue {
+				if low, ok := low.(*Int); ok {
+					lowIdx = low.Value
+				} else {
+					v.err = fmt.Errorf("invalid slice index type: %s",
+						low.TypeName())
+					return
+				}
+			}
+
+			switch left := left.(type) {
+			case *Array:
+				numElements := int64(len(left.Value))
+				var highIdx int64
+				if high == UndefinedValue {
+					highIdx = numElements
+				} else if high, ok := high.(*Int); ok {
+					highIdx = high.Value
+				} else {
+					v.err = fmt.Errorf("invalid slice index type: %s",
+						high.TypeName())
+					return
+				}
+				if lowIdx > highIdx {
+					v.err = fmt.Errorf("invalid slice index: %d > %d",
+						lowIdx, highIdx)
+					return
+				}
+				if lowIdx < 0 {
+					lowIdx = 0
+				} else if lowIdx > numElements {
+					lowIdx = numElements
+				}
+				if highIdx < 0 {
+					highIdx = 0
+				} else if highIdx > numElements {
+					highIdx = numElements
+				}
+				var val Object = &Array{
+					Value: left.Value[lowIdx:highIdx],
+				}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp] = val
+				v.sp++
+			case *ImmutableArray:
+				numElements := int64(len(left.Value))
+				var highIdx int64
+				if high == UndefinedValue {
+					highIdx = numElements
+				} else if high, ok := high.(*Int); ok {
+					highIdx = high.Value
+				} else {
+					v.err = fmt.Errorf("invalid slice index type: %s",
+						high.TypeName())
+					return
+				}
+				if lowIdx > highIdx {
+					v.err = fmt.Errorf("invalid slice index: %d > %d",
+						lowIdx, highIdx)
+					return
+				}
+				if lowIdx < 0 {
+					lowIdx = 0
+				} else if lowIdx > numElements {
+					lowIdx = numElements
+				}
+				if highIdx < 0 {
+					highIdx = 0
+				} else if highIdx > numElements {
+					highIdx = numElements
+				}
+				var val Object = &Array{
+					Value: left.Value[lowIdx:highIdx],
+				}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp] = val
+				v.sp++
+			case *String:
+				numElements := int64(len(left.Value))
+				var highIdx int64
+				if high == UndefinedValue {
+					highIdx = numElements
+				} else if high, ok := high.(*Int); ok {
+					highIdx = high.Value
+				} else {
+					v.err = fmt.Errorf("invalid slice index type: %s",
+						high.TypeName())
+					return
+				}
+				if lowIdx > highIdx {
+					v.err = fmt.Errorf("invalid slice index: %d > %d",
+						lowIdx, highIdx)
+					return
+				}
+				if lowIdx < 0 {
+					lowIdx = 0
+				} else if lowIdx > numElements {
+					lowIdx = numElements
+				}
+				if highIdx < 0 {
+					highIdx = 0
+				} else if highIdx > numElements {
+					highIdx = numElements
+				}
+				var val Object = &String{
+					Value: left.Value[lowIdx:highIdx],
+				}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp] = val
+				v.sp++
+			case *Bytes:
+				numElements := int64(len(left.Value))
+				var highIdx int64
+				if high == UndefinedValue {
+					highIdx = numElements
+				} else if high, ok := high.(*Int); ok {
+					highIdx = high.Value
+				} else {
+					v.err = fmt.Errorf("invalid slice index type: %s",
+						high.TypeName())
+					return
+				}
+				if lowIdx > highIdx {
+					v.err = fmt.Errorf("invalid slice index: %d > %d",
+						lowIdx, highIdx)
+					return
+				}
+				if lowIdx < 0 {
+					lowIdx = 0
+				} else if lowIdx > numElements {
+					lowIdx = numElements
+				}
+				if highIdx < 0 {
+					highIdx = 0
+				} else if highIdx > numElements {
+					highIdx = numElements
+				}
+				var val Object = &Bytes{
+					Value: left.Value[lowIdx:highIdx],
+				}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp] = val
+				v.sp++
+			}
+		case parser.OpCall:
+			numArgs := int(v.curInsts[v.ip+1])
+			v.ip++
+			value := v.stack[v.sp-1-numArgs]
+			if !value.CanCall() {
+				v.err = fmt.Errorf("not callable: %s", value.TypeName())
+				return
+			}
+			if callee, ok := value.(*CompiledFunction); ok {
+				if callee.VarArgs {
+					// if the closure is variadic,
+					// roll up all variadic parameters into an array
+					realArgs := callee.NumParameters - 1
+					varArgs := numArgs - realArgs
+					if varArgs >= 0 {
+						numArgs = realArgs + 1
+						args := make([]Object, varArgs)
+						spStart := v.sp - varArgs
+						for i := spStart; i < v.sp; i++ {
+							args[i-spStart] = v.stack[i]
+						}
+						v.stack[spStart] = &Array{Value: args}
+						v.sp = spStart + 1
+					}
+				}
+				if numArgs != callee.NumParameters {
+					if callee.VarArgs {
+						v.err = fmt.Errorf(
+							"wrong number of arguments: want>=%d, got=%d",
+							callee.NumParameters-1, numArgs)
+					} else {
+						v.err = fmt.Errorf(
+							"wrong number of arguments: want=%d, got=%d",
+							callee.NumParameters, numArgs)
+					}
+					return
+				}
+
+				// test if it's tail-call
+				if callee == v.curFrame.fn { // recursion
+					nextOp := v.curInsts[v.ip+1]
+					if nextOp == parser.OpReturn ||
+						(nextOp == parser.OpPop &&
+							parser.OpReturn == v.curInsts[v.ip+2]) {
+						for p := 0; p < numArgs; p++ {
+							v.stack[v.curFrame.basePointer+p] =
+								v.stack[v.sp-numArgs+p]
+						}
+						v.sp -= numArgs + 1
+						v.ip = -1 // reset IP to beginning of the frame
+						continue
+					}
+				}
+				if v.framesIndex >= MaxFrames {
+					v.err = ErrStackOverflow
+					return
+				}
+
+				// update call frame
+				v.curFrame.ip = v.ip // store current ip before call
+				v.curFrame = &(v.frames[v.framesIndex])
+				v.curFrame.fn = callee
+				v.curFrame.freeVars = callee.Free
+				v.curFrame.basePointer = v.sp - numArgs
+				v.curInsts = callee.Instructions
+				v.ip = -1
+				v.framesIndex++
+				v.sp = v.sp - numArgs + callee.NumLocals
+			} else {
+				var args []Object
+				args = append(args, v.stack[v.sp-numArgs:v.sp]...)
+				ret, e := value.Call(args...)
+				v.sp -= numArgs + 1
+
+				// runtime error
+				if e != nil {
+					if e == ErrWrongNumArguments {
+						v.err = fmt.Errorf(
+							"wrong number of arguments in call to '%s'",
+							value.TypeName())
+						return
+					}
+					if e, ok := e.(ErrInvalidArgumentType); ok {
+						v.err = fmt.Errorf(
+							"invalid type for argument '%s' in call to '%s': "+
+								"expected %s, found %s",
+							e.Name, value.TypeName(), e.Expected, e.Found)
+						return
+					}
+					v.err = e
+					return
+				}
+
+				// nil return -> undefined
+				if ret == nil {
+					ret = UndefinedValue
+				}
+				v.allocs--
+				if v.allocs == 0 {
+					v.err = ErrObjectAllocLimit
+					return
+				}
+				v.stack[v.sp] = ret
+				v.sp++
+			}
+		case parser.OpReturn:
+			v.ip++
+			var retVal Object
+			if int(v.curInsts[v.ip]) == 1 {
+				retVal = v.stack[v.sp-1]
+			} else {
+				retVal = UndefinedValue
+			}
+			//v.sp--
+			v.framesIndex--
+			v.curFrame = &v.frames[v.framesIndex-1]
+			v.curInsts = v.curFrame.fn.Instructions
+			v.ip = v.curFrame.ip
+			//v.sp = lastFrame.basePointer - 1
+			v.sp = v.frames[v.framesIndex].basePointer
+			// skip stack overflow check because (newSP) <= (oldSP)
+			v.stack[v.sp-1] = retVal
+			//v.sp++
+		case parser.OpDefineLocal:
+			v.ip++
+			localIndex := int(v.curInsts[v.ip])
+			sp := v.curFrame.basePointer + localIndex
+
+			// local variables can be mutated by other actions
+			// so always store the copy of popped value
+			val := v.stack[v.sp-1]
+			v.sp--
+			v.stack[sp] = val
+		case parser.OpSetLocal:
+			localIndex := int(v.curInsts[v.ip+1])
+			v.ip++
+			sp := v.curFrame.basePointer + localIndex
+
+			// update pointee of v.stack[sp] instead of replacing the pointer
+			// itself. this is needed because there can be free variables
+			// referencing the same local variables.
+			val := v.stack[v.sp-1]
+			v.sp--
+			if obj, ok := v.stack[sp].(*ObjectPtr); ok {
+				*obj.Value = val
+				val = obj
+			}
+			v.stack[sp] = val // also use a copy of popped value
+		case parser.OpSetSelLocal:
+			localIndex := int(v.curInsts[v.ip+1])
+			numSelectors := int(v.curInsts[v.ip+2])
+			v.ip += 2
+
+			// selectors and RHS value
+			selectors := make([]Object, numSelectors)
+			for i := 0; i < numSelectors; i++ {
+				selectors[i] = v.stack[v.sp-numSelectors+i]
+			}
+			val := v.stack[v.sp-numSelectors-1]
+			v.sp -= numSelectors + 1
+			dst := v.stack[v.curFrame.basePointer+localIndex]
+			if obj, ok := dst.(*ObjectPtr); ok {
+				dst = *obj.Value
+			}
+			if e := indexAssign(dst, val, selectors); e != nil {
+				v.err = e
+				return
+			}
+		case parser.OpGetLocal:
+			v.ip++
+			localIndex := int(v.curInsts[v.ip])
+			val := v.stack[v.curFrame.basePointer+localIndex]
+			if obj, ok := val.(*ObjectPtr); ok {
+				val = *obj.Value
+			}
+			v.stack[v.sp] = val
+			v.sp++
+		case parser.OpGetBuiltin:
+			v.ip++
+			builtinIndex := int(v.curInsts[v.ip])
+			v.stack[v.sp] = builtinFuncs[builtinIndex]
+			v.sp++
+		case parser.OpClosure:
+			v.ip += 3
+			constIndex := int(v.curInsts[v.ip-1]) | int(v.curInsts[v.ip-2])<<8
+			numFree := int(v.curInsts[v.ip])
+			fn, ok := v.constants[constIndex].(*CompiledFunction)
+			if !ok {
+				v.err = fmt.Errorf("not function: %s", fn.TypeName())
+				return
+			}
+			free := make([]*ObjectPtr, numFree)
+			for i := 0; i < numFree; i++ {
+				switch freeVar := (v.stack[v.sp-numFree+i]).(type) {
+				case *ObjectPtr:
+					free[i] = freeVar
+				default:
+					free[i] = &ObjectPtr{
+						Value: &v.stack[v.sp-numFree+i],
+					}
+				}
+			}
+			v.sp -= numFree
+			cl := &CompiledFunction{
+				Instructions:  fn.Instructions,
+				NumLocals:     fn.NumLocals,
+				NumParameters: fn.NumParameters,
+				VarArgs:       fn.VarArgs,
+				Free:          free,
+			}
+			v.allocs--
+			if v.allocs == 0 {
+				v.err = ErrObjectAllocLimit
+				return
+			}
+			v.stack[v.sp] = cl
+			v.sp++
+		case parser.OpGetFreePtr:
+			v.ip++
+			freeIndex := int(v.curInsts[v.ip])
+			val := v.curFrame.freeVars[freeIndex]
+			v.stack[v.sp] = val
+			v.sp++
+		case parser.OpGetFree:
+			v.ip++
+			freeIndex := int(v.curInsts[v.ip])
+			val := *v.curFrame.freeVars[freeIndex].Value
+			v.stack[v.sp] = val
+			v.sp++
+		case parser.OpSetFree:
+			v.ip++
+			freeIndex := int(v.curInsts[v.ip])
+			*v.curFrame.freeVars[freeIndex].Value = v.stack[v.sp-1]
+			v.sp--
+		case parser.OpGetLocalPtr:
+			v.ip++
+			localIndex := int(v.curInsts[v.ip])
+			sp := v.curFrame.basePointer + localIndex
+			val := v.stack[sp]
+			var freeVar *ObjectPtr
+			if obj, ok := val.(*ObjectPtr); ok {
+				freeVar = obj
+			} else {
+				freeVar = &ObjectPtr{Value: &val}
+				v.stack[sp] = freeVar
+			}
+			v.stack[v.sp] = freeVar
+			v.sp++
+		case parser.OpSetSelFree:
+			v.ip += 2
+			freeIndex := int(v.curInsts[v.ip-1])
+			numSelectors := int(v.curInsts[v.ip])
+
+			// selectors and RHS value
+			selectors := make([]Object, numSelectors)
+			for i := 0; i < numSelectors; i++ {
+				selectors[i] = v.stack[v.sp-numSelectors+i]
+			}
+			val := v.stack[v.sp-numSelectors-1]
+			v.sp -= numSelectors + 1
+			e := indexAssign(*v.curFrame.freeVars[freeIndex].Value,
+				val, selectors)
+			if e != nil {
+				v.err = e
+				return
+			}
+		case parser.OpIteratorInit:
+			var iterator Object
+			dst := v.stack[v.sp-1]
+			v.sp--
+			if !dst.CanIterate() {
+				v.err = fmt.Errorf("not iterable: %s", dst.TypeName())
+				return
+			}
+			iterator = dst.Iterate()
+			v.allocs--
+			if v.allocs == 0 {
+				v.err = ErrObjectAllocLimit
+				return
+			}
+			v.stack[v.sp] = iterator
+			v.sp++
+		case parser.OpIteratorNext:
+			iterator := v.stack[v.sp-1]
+			v.sp--
+			hasMore := iterator.(Iterator).Next()
+			if hasMore {
+				v.stack[v.sp] = TrueValue
+			} else {
+				v.stack[v.sp] = FalseValue
+			}
+			v.sp++
+		case parser.OpIteratorKey:
+			iterator := v.stack[v.sp-1]
+			v.sp--
+			val := iterator.(Iterator).Key()
+			v.stack[v.sp] = val
+			v.sp++
+		case parser.OpIteratorValue:
+			iterator := v.stack[v.sp-1]
+			v.sp--
+			val := iterator.(Iterator).Value()
+			v.stack[v.sp] = val
+			v.sp++
+		case parser.OpSuspend:
+			return
+		default:
+			v.err = fmt.Errorf("unknown opcode: %d", v.curInsts[v.ip])
+			return
+		}
+	}
+}
+
+// IsStackEmpty tests if the stack is empty or not.
+func (v *VM) IsStackEmpty() bool {
+	return v.sp == 0
+}
+
+func indexAssign(dst, src Object, selectors []Object) error {
+	numSel := len(selectors)
+	for sidx := numSel - 1; sidx > 0; sidx-- {
+		next, err := dst.IndexGet(selectors[sidx])
+		if err != nil {
+			if err == ErrNotIndexable {
+				return fmt.Errorf("not indexable: %s", dst.TypeName())
+			}
+			if err == ErrInvalidIndexType {
+				return fmt.Errorf("invalid index type: %s",
+					selectors[sidx].TypeName())
+			}
+			return err
+		}
+		dst = next
+	}
+
+	if err := dst.IndexSet(selectors[0], src); err != nil {
+		if err == ErrNotIndexAssignable {
+			return fmt.Errorf("not index-assignable: %s", dst.TypeName())
+		}
+		if err == ErrInvalidIndexValueType {
+			return fmt.Errorf("invaid index value type: %s", src.TypeName())
+		}
+		return err
+	}
+	return nil
+}