Add scripting (tengo) support for every incoming message (#731)

TengoModifyMessage allows you to specify the location of a tengo (https://github.com/d5/tengo/) script.
This script will receive every incoming message and can be used to modify the Username and the Text of that message.
The script will have the following global variables:
to modify: msgUsername and msgText
to read: msgChannel and msgAccount

The script is reloaded on every message, so you can modify the script on the fly.

Example script can be found in https://github.com/42wim/matterbridge/tree/master/gateway/bench.tengo
and https://github.com/42wim/matterbridge/tree/master/contrib/example.tengo

The example below will check if the text contains blah and if so, it'll replace the text and the username of that message.
text := import("text")
if text.re_match("blah",msgText) {
    msgText="replaced by this"
    msgUsername="fakeuser"
}

More information about tengo on: https://github.com/d5/tengo/blob/master/docs/tutorial.md and
https://github.com/d5/tengo/blob/master/docs/stdlib.md

3 files changed, 1445 insertions, 0 deletions

diff --git a/vendor/github.com/d5/tengo/runtime/errors.go b/vendor/github.com/d5/tengo/runtime/errors.go
new file mode 100644
index 00000000..f5f201ce
--- /dev/null
+++ b/vendor/github.com/d5/tengo/runtime/errors.go
@@ -0,0 +1,8 @@
+package runtime
+
+import (
+	"errors"
+)
+
+// ErrStackOverflow is a stack overflow error.
+var ErrStackOverflow = errors.New("stack overflow")
diff --git a/vendor/github.com/d5/tengo/runtime/frame.go b/vendor/github.com/d5/tengo/runtime/frame.go
new file mode 100644
index 00000000..90151a1e
--- /dev/null
+++ b/vendor/github.com/d5/tengo/runtime/frame.go
@@ -0,0 +1,13 @@
+package runtime
+
+import (
+	"github.com/d5/tengo/objects"
+)
+
+// Frame represents a function call frame.
+type Frame struct {
+	fn          *objects.CompiledFunction
+	freeVars    []*objects.Object
+	ip          int
+	basePointer int
+}
diff --git a/vendor/github.com/d5/tengo/runtime/vm.go b/vendor/github.com/d5/tengo/runtime/vm.go
new file mode 100644
index 00000000..2708fde7
--- /dev/null
+++ b/vendor/github.com/d5/tengo/runtime/vm.go
@@ -0,0 +1,1424 @@
+package runtime
+
+import (
+	"fmt"
+	"sync/atomic"
+
+	"github.com/d5/tengo/compiler"
+	"github.com/d5/tengo/compiler/source"
+	"github.com/d5/tengo/compiler/token"
+	"github.com/d5/tengo/objects"
+	"github.com/d5/tengo/stdlib"
+)
+
+const (
+	// StackSize is the maximum stack size.
+	StackSize = 2048
+
+	// GlobalsSize is the maximum number of global variables.
+	GlobalsSize = 1024
+
+	// MaxFrames is the maximum number of function frames.
+	MaxFrames = 1024
+)
+
+var (
+	truePtr      = &objects.TrueValue
+	falsePtr     = &objects.FalseValue
+	undefinedPtr = &objects.UndefinedValue
+	builtinFuncs []objects.Object
+)
+
+// VM is a virtual machine that executes the bytecode compiled by Compiler.
+type VM struct {
+	constants      []objects.Object
+	stack          []*objects.Object
+	sp             int
+	globals        []*objects.Object
+	fileSet        *source.FileSet
+	frames         []Frame
+	framesIndex    int
+	curFrame       *Frame
+	curInsts       []byte
+	curIPLimit     int
+	ip             int
+	aborting       int64
+	builtinModules map[string]*objects.Object
+}
+
+// NewVM creates a VM.
+func NewVM(bytecode *compiler.Bytecode, globals []*objects.Object, builtinModules map[string]*objects.Object) *VM {
+	if globals == nil {
+		globals = make([]*objects.Object, GlobalsSize)
+	}
+
+	if builtinModules == nil {
+		builtinModules = stdlib.Modules
+	}
+
+	frames := make([]Frame, MaxFrames)
+	frames[0].fn = bytecode.MainFunction
+	frames[0].freeVars = nil
+	frames[0].ip = -1
+	frames[0].basePointer = 0
+
+	return &VM{
+		constants:      bytecode.Constants,
+		stack:          make([]*objects.Object, StackSize),
+		sp:             0,
+		globals:        globals,
+		fileSet:        bytecode.FileSet,
+		frames:         frames,
+		framesIndex:    1,
+		curFrame:       &(frames[0]),
+		curInsts:       frames[0].fn.Instructions,
+		curIPLimit:     len(frames[0].fn.Instructions) - 1,
+		ip:             -1,
+		builtinModules: builtinModules,
+	}
+}
+
+// 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.curIPLimit = len(v.curInsts) - 1
+	v.framesIndex = 1
+	v.ip = -1
+	atomic.StoreInt64(&v.aborting, 0)
+
+	var filePos source.FilePos
+
+mainloop:
+	for v.ip < v.curIPLimit && (atomic.LoadInt64(&v.aborting) == 0) {
+		v.ip++
+
+		switch v.curInsts[v.ip] {
+		case compiler.OpConstant:
+			cidx := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip += 2
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &v.constants[cidx]
+			v.sp++
+
+		case compiler.OpNull:
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = undefinedPtr
+			v.sp++
+
+		case compiler.OpAdd:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Add, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s + %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpSub:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Sub, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s - %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpMul:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Mul, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s * %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpDiv:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Quo, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s / %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpRem:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Rem, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s %% %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpBAnd:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.And, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s & %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpBOr:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Or, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s | %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpBXor:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Xor, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s ^ %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpBAndNot:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.AndNot, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s &^ %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpBShiftLeft:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Shl, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s << %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpBShiftRight:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Shr, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s >> %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpEqual:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			if (*left).Equals(*right) {
+				v.stack[v.sp] = truePtr
+			} else {
+				v.stack[v.sp] = falsePtr
+			}
+			v.sp++
+
+		case compiler.OpNotEqual:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			if (*left).Equals(*right) {
+				v.stack[v.sp] = falsePtr
+			} else {
+				v.stack[v.sp] = truePtr
+			}
+			v.sp++
+
+		case compiler.OpGreaterThan:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.Greater, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s > %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpGreaterThanEqual:
+			right := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			res, e := (*left).BinaryOp(token.GreaterEq, *right)
+			if e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				if e == objects.ErrInvalidOperator {
+					err = fmt.Errorf("invalid operation: %s >= %s",
+						(*left).TypeName(), (*right).TypeName())
+					break mainloop
+				}
+
+				err = e
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &res
+			v.sp++
+
+		case compiler.OpPop:
+			v.sp--
+
+		case compiler.OpTrue:
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = truePtr
+			v.sp++
+
+		case compiler.OpFalse:
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = falsePtr
+			v.sp++
+
+		case compiler.OpLNot:
+			operand := v.stack[v.sp-1]
+			v.sp--
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			if (*operand).IsFalsy() {
+				v.stack[v.sp] = truePtr
+			} else {
+				v.stack[v.sp] = falsePtr
+			}
+			v.sp++
+
+		case compiler.OpBComplement:
+			operand := v.stack[v.sp-1]
+			v.sp--
+
+			switch x := (*operand).(type) {
+			case *objects.Int:
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				var res objects.Object = &objects.Int{Value: ^x.Value}
+
+				v.stack[v.sp] = &res
+				v.sp++
+			default:
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				err = fmt.Errorf("invalid operation: ^%s", (*operand).TypeName())
+				break mainloop
+			}
+
+		case compiler.OpMinus:
+			operand := v.stack[v.sp-1]
+			v.sp--
+
+			switch x := (*operand).(type) {
+			case *objects.Int:
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				var res objects.Object = &objects.Int{Value: -x.Value}
+
+				v.stack[v.sp] = &res
+				v.sp++
+			case *objects.Float:
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				var res objects.Object = &objects.Float{Value: -x.Value}
+
+				v.stack[v.sp] = &res
+				v.sp++
+			default:
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				err = fmt.Errorf("invalid operation: -%s", (*operand).TypeName())
+				break mainloop
+			}
+
+		case compiler.OpJumpFalsy:
+			pos := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip += 2
+
+			condition := v.stack[v.sp-1]
+			v.sp--
+
+			if (*condition).IsFalsy() {
+				v.ip = pos - 1
+			}
+
+		case compiler.OpAndJump:
+			pos := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip += 2
+
+			condition := *v.stack[v.sp-1]
+			if condition.IsFalsy() {
+				v.ip = pos - 1
+			} else {
+				v.sp--
+			}
+
+		case compiler.OpOrJump:
+			pos := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip += 2
+
+			condition := *v.stack[v.sp-1]
+			if !condition.IsFalsy() {
+				v.ip = pos - 1
+			} else {
+				v.sp--
+			}
+
+		case compiler.OpJump:
+			pos := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip = pos - 1
+
+		case compiler.OpSetGlobal:
+			globalIndex := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip += 2
+
+			v.sp--
+
+			v.globals[globalIndex] = v.stack[v.sp]
+
+		case compiler.OpSetSelGlobal:
+			globalIndex := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			numSelectors := int(v.curInsts[v.ip+3])
+			v.ip += 3
+
+			// selectors and RHS value
+			selectors := v.stack[v.sp-numSelectors : v.sp]
+			val := v.stack[v.sp-numSelectors-1]
+			v.sp -= numSelectors + 1
+
+			if e := indexAssign(v.globals[globalIndex], val, selectors); e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip-3])
+				err = e
+				break mainloop
+			}
+
+		case compiler.OpGetGlobal:
+			globalIndex := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip += 2
+
+			val := v.globals[globalIndex]
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = val
+			v.sp++
+
+		case compiler.OpArray:
+			numElements := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip += 2
+
+			var elements []objects.Object
+			for i := v.sp - numElements; i < v.sp; i++ {
+				elements = append(elements, *v.stack[i])
+			}
+			v.sp -= numElements
+
+			var arr objects.Object = &objects.Array{Value: elements}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &arr
+			v.sp++
+
+		case compiler.OpMap:
+			numElements := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			v.ip += 2
+
+			kv := make(map[string]objects.Object)
+			for i := v.sp - numElements; i < v.sp; i += 2 {
+				key := *v.stack[i]
+				value := *v.stack[i+1]
+				kv[key.(*objects.String).Value] = value
+			}
+			v.sp -= numElements
+
+			var m objects.Object = &objects.Map{Value: kv}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &m
+			v.sp++
+
+		case compiler.OpError:
+			value := v.stack[v.sp-1]
+
+			var e objects.Object = &objects.Error{
+				Value: *value,
+			}
+
+			v.stack[v.sp-1] = &e
+
+		case compiler.OpImmutable:
+			value := v.stack[v.sp-1]
+
+			switch value := (*value).(type) {
+			case *objects.Array:
+				var immutableArray objects.Object = &objects.ImmutableArray{
+					Value: value.Value,
+				}
+				v.stack[v.sp-1] = &immutableArray
+			case *objects.Map:
+				var immutableMap objects.Object = &objects.ImmutableMap{
+					Value: value.Value,
+				}
+				v.stack[v.sp-1] = &immutableMap
+			}
+
+		case compiler.OpIndex:
+			index := v.stack[v.sp-1]
+			left := v.stack[v.sp-2]
+			v.sp -= 2
+
+			switch left := (*left).(type) {
+			case objects.Indexable:
+				val, e := left.IndexGet(*index)
+				if e != nil {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+
+					if e == objects.ErrInvalidIndexType {
+						err = fmt.Errorf("invalid index type: %s", (*index).TypeName())
+						break mainloop
+					}
+
+					err = e
+					break mainloop
+				}
+				if val == nil {
+					val = objects.UndefinedValue
+				}
+
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				v.stack[v.sp] = &val
+				v.sp++
+
+			case *objects.Error: // e.value
+				key, ok := (*index).(*objects.String)
+				if !ok || key.Value != "value" {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid index on error")
+					break mainloop
+				}
+
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				v.stack[v.sp] = &left.Value
+				v.sp++
+
+			default:
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				err = fmt.Errorf("not indexable: %s", left.TypeName())
+				break mainloop
+			}
+
+		case compiler.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 != objects.UndefinedValue {
+				if low, ok := (*low).(*objects.Int); ok {
+					lowIdx = low.Value
+				} else {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid slice index type: %s", low.TypeName())
+					break mainloop
+				}
+			}
+
+			switch left := (*left).(type) {
+			case *objects.Array:
+				numElements := int64(len(left.Value))
+				var highIdx int64
+				if *high == objects.UndefinedValue {
+					highIdx = numElements
+				} else if high, ok := (*high).(*objects.Int); ok {
+					highIdx = high.Value
+				} else {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid slice index type: %s", high.TypeName())
+					break mainloop
+				}
+
+				if lowIdx > highIdx {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid slice index: %d > %d", lowIdx, highIdx)
+					break mainloop
+				}
+
+				if lowIdx < 0 {
+					lowIdx = 0
+				} else if lowIdx > numElements {
+					lowIdx = numElements
+				}
+
+				if highIdx < 0 {
+					highIdx = 0
+				} else if highIdx > numElements {
+					highIdx = numElements
+				}
+
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				var val objects.Object = &objects.Array{Value: left.Value[lowIdx:highIdx]}
+				v.stack[v.sp] = &val
+				v.sp++
+
+			case *objects.ImmutableArray:
+				numElements := int64(len(left.Value))
+				var highIdx int64
+				if *high == objects.UndefinedValue {
+					highIdx = numElements
+				} else if high, ok := (*high).(*objects.Int); ok {
+					highIdx = high.Value
+				} else {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid slice index type: %s", high.TypeName())
+					break mainloop
+				}
+
+				if lowIdx > highIdx {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid slice index: %d > %d", lowIdx, highIdx)
+					break mainloop
+				}
+
+				if lowIdx < 0 {
+					lowIdx = 0
+				} else if lowIdx > numElements {
+					lowIdx = numElements
+				}
+
+				if highIdx < 0 {
+					highIdx = 0
+				} else if highIdx > numElements {
+					highIdx = numElements
+				}
+
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				var val objects.Object = &objects.Array{Value: left.Value[lowIdx:highIdx]}
+
+				v.stack[v.sp] = &val
+				v.sp++
+
+			case *objects.String:
+				numElements := int64(len(left.Value))
+				var highIdx int64
+				if *high == objects.UndefinedValue {
+					highIdx = numElements
+				} else if high, ok := (*high).(*objects.Int); ok {
+					highIdx = high.Value
+				} else {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid slice index type: %s", high.TypeName())
+					break mainloop
+				}
+
+				if lowIdx > highIdx {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid slice index: %d > %d", lowIdx, highIdx)
+					break mainloop
+				}
+
+				if lowIdx < 0 {
+					lowIdx = 0
+				} else if lowIdx > numElements {
+					lowIdx = numElements
+				}
+
+				if highIdx < 0 {
+					highIdx = 0
+				} else if highIdx > numElements {
+					highIdx = numElements
+				}
+
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				var val objects.Object = &objects.String{Value: left.Value[lowIdx:highIdx]}
+
+				v.stack[v.sp] = &val
+				v.sp++
+
+			case *objects.Bytes:
+				numElements := int64(len(left.Value))
+				var highIdx int64
+				if *high == objects.UndefinedValue {
+					highIdx = numElements
+				} else if high, ok := (*high).(*objects.Int); ok {
+					highIdx = high.Value
+				} else {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid slice index type: %s", high.TypeName())
+					break mainloop
+				}
+
+				if lowIdx > highIdx {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+					err = fmt.Errorf("invalid slice index: %d > %d", lowIdx, highIdx)
+					break mainloop
+				}
+
+				if lowIdx < 0 {
+					lowIdx = 0
+				} else if lowIdx > numElements {
+					lowIdx = numElements
+				}
+
+				if highIdx < 0 {
+					highIdx = 0
+				} else if highIdx > numElements {
+					highIdx = numElements
+				}
+
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				var val objects.Object = &objects.Bytes{Value: left.Value[lowIdx:highIdx]}
+
+				v.stack[v.sp] = &val
+				v.sp++
+			}
+
+		case compiler.OpCall:
+			numArgs := int(v.curInsts[v.ip+1])
+			v.ip++
+
+			value := *v.stack[v.sp-1-numArgs]
+
+			switch callee := value.(type) {
+			case *objects.Closure:
+				if numArgs != callee.Fn.NumParameters {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip-1])
+					err = fmt.Errorf("wrong number of arguments: want=%d, got=%d",
+						callee.Fn.NumParameters, numArgs)
+					break mainloop
+				}
+
+				// test if it's tail-call
+				if callee.Fn == v.curFrame.fn { // recursion
+					nextOp := v.curInsts[v.ip+1]
+					if nextOp == compiler.OpReturnValue ||
+						(nextOp == compiler.OpPop && compiler.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 mainloop
+					}
+				}
+
+				// update call frame
+				v.curFrame.ip = v.ip // store current ip before call
+				v.curFrame = &(v.frames[v.framesIndex])
+				v.curFrame.fn = callee.Fn
+				v.curFrame.freeVars = callee.Free
+				v.curFrame.basePointer = v.sp - numArgs
+				v.curInsts = callee.Fn.Instructions
+				v.ip = -1
+				v.curIPLimit = len(v.curInsts) - 1
+				v.framesIndex++
+				v.sp = v.sp - numArgs + callee.Fn.NumLocals
+
+			case *objects.CompiledFunction:
+				if numArgs != callee.NumParameters {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip-1])
+					err = fmt.Errorf("wrong number of arguments: want=%d, got=%d",
+						callee.NumParameters, numArgs)
+					break mainloop
+				}
+
+				// test if it's tail-call
+				if callee == v.curFrame.fn { // recursion
+					nextOp := v.curInsts[v.ip+1]
+					if nextOp == compiler.OpReturnValue ||
+						(nextOp == compiler.OpPop && compiler.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 mainloop
+					}
+				}
+
+				// 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 = nil
+				v.curFrame.basePointer = v.sp - numArgs
+				v.curInsts = callee.Instructions
+				v.ip = -1
+				v.curIPLimit = len(v.curInsts) - 1
+				v.framesIndex++
+				v.sp = v.sp - numArgs + callee.NumLocals
+
+			case objects.Callable:
+				var args []objects.Object
+				for _, arg := range v.stack[v.sp-numArgs : v.sp] {
+					args = append(args, *arg)
+				}
+
+				ret, e := callee.Call(args...)
+				v.sp -= numArgs + 1
+
+				// runtime error
+				if e != nil {
+					filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip-1])
+
+					if e == objects.ErrWrongNumArguments {
+						err = fmt.Errorf("wrong number of arguments in call to '%s'",
+							value.TypeName())
+						break mainloop
+					}
+
+					if e, ok := e.(objects.ErrInvalidArgumentType); ok {
+						err = fmt.Errorf("invalid type for argument '%s' in call to '%s': expected %s, found %s",
+							e.Name, value.TypeName(), e.Expected, e.Found)
+						break mainloop
+					}
+
+					err = e
+					break mainloop
+				}
+
+				// nil return -> undefined
+				if ret == nil {
+					ret = objects.UndefinedValue
+				}
+
+				if v.sp >= StackSize {
+					err = ErrStackOverflow
+					break mainloop
+				}
+
+				v.stack[v.sp] = &ret
+				v.sp++
+
+			default:
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip-1])
+				err = fmt.Errorf("not callable: %s", callee.TypeName())
+				break mainloop
+			}
+
+		case compiler.OpReturnValue:
+			retVal := v.stack[v.sp-1]
+			//v.sp--
+
+			v.framesIndex--
+			lastFrame := v.frames[v.framesIndex]
+			v.curFrame = &v.frames[v.framesIndex-1]
+			v.curInsts = v.curFrame.fn.Instructions
+			v.curIPLimit = len(v.curInsts) - 1
+			v.ip = v.curFrame.ip
+
+			//v.sp = lastFrame.basePointer - 1
+			v.sp = lastFrame.basePointer
+
+			// skip stack overflow check because (newSP) <= (oldSP)
+			v.stack[v.sp-1] = retVal
+			//v.sp++
+
+		case compiler.OpReturn:
+			v.framesIndex--
+			lastFrame := v.frames[v.framesIndex]
+			v.curFrame = &v.frames[v.framesIndex-1]
+			v.curInsts = v.curFrame.fn.Instructions
+			v.curIPLimit = len(v.curInsts) - 1
+			v.ip = v.curFrame.ip
+
+			//v.sp = lastFrame.basePointer - 1
+			v.sp = lastFrame.basePointer
+
+			// skip stack overflow check because (newSP) <= (oldSP)
+			v.stack[v.sp-1] = undefinedPtr
+			//v.sp++
+
+		case compiler.OpDefineLocal:
+			localIndex := int(v.curInsts[v.ip+1])
+			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 compiler.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--
+
+			*v.stack[sp] = *val // also use a copy of popped value
+
+		case compiler.OpSetSelLocal:
+			localIndex := int(v.curInsts[v.ip+1])
+			numSelectors := int(v.curInsts[v.ip+2])
+			v.ip += 2
+
+			// selectors and RHS value
+			selectors := v.stack[v.sp-numSelectors : v.sp]
+			val := v.stack[v.sp-numSelectors-1]
+			v.sp -= numSelectors + 1
+
+			sp := v.curFrame.basePointer + localIndex
+
+			if e := indexAssign(v.stack[sp], val, selectors); e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip-2])
+				err = e
+				break mainloop
+			}
+
+		case compiler.OpGetLocal:
+			localIndex := int(v.curInsts[v.ip+1])
+			v.ip++
+
+			val := v.stack[v.curFrame.basePointer+localIndex]
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = val
+			v.sp++
+
+		case compiler.OpGetBuiltin:
+			builtinIndex := int(v.curInsts[v.ip+1])
+			v.ip++
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &builtinFuncs[builtinIndex]
+			v.sp++
+
+		case compiler.OpGetBuiltinModule:
+			val := v.stack[v.sp-1]
+			v.sp--
+
+			moduleName := (*val).(*objects.String).Value
+
+			module, ok := v.builtinModules[moduleName]
+			if !ok {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip-3])
+				err = fmt.Errorf("module '%s' not found", moduleName)
+				break mainloop
+			}
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = module
+			v.sp++
+
+		case compiler.OpClosure:
+			constIndex := int(v.curInsts[v.ip+2]) | int(v.curInsts[v.ip+1])<<8
+			numFree := int(v.curInsts[v.ip+3])
+			v.ip += 3
+
+			fn, ok := v.constants[constIndex].(*objects.CompiledFunction)
+			if !ok {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip-3])
+				err = fmt.Errorf("not function: %s", fn.TypeName())
+				break mainloop
+			}
+
+			free := make([]*objects.Object, numFree)
+			for i := 0; i < numFree; i++ {
+				free[i] = v.stack[v.sp-numFree+i]
+			}
+			v.sp -= numFree
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			var cl objects.Object = &objects.Closure{
+				Fn:   fn,
+				Free: free,
+			}
+
+			v.stack[v.sp] = &cl
+			v.sp++
+
+		case compiler.OpGetFree:
+			freeIndex := int(v.curInsts[v.ip+1])
+			v.ip++
+
+			val := v.curFrame.freeVars[freeIndex]
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = val
+			v.sp++
+
+		case compiler.OpSetSelFree:
+			freeIndex := int(v.curInsts[v.ip+1])
+			numSelectors := int(v.curInsts[v.ip+2])
+			v.ip += 2
+
+			// selectors and RHS value
+			selectors := v.stack[v.sp-numSelectors : v.sp]
+			val := v.stack[v.sp-numSelectors-1]
+			v.sp -= numSelectors + 1
+
+			if e := indexAssign(v.curFrame.freeVars[freeIndex], val, selectors); e != nil {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip-2])
+				err = e
+				break mainloop
+			}
+
+		case compiler.OpSetFree:
+			freeIndex := int(v.curInsts[v.ip+1])
+			v.ip++
+
+			val := v.stack[v.sp-1]
+			v.sp--
+
+			*v.curFrame.freeVars[freeIndex] = *val
+
+		case compiler.OpIteratorInit:
+			var iterator objects.Object
+
+			dst := v.stack[v.sp-1]
+			v.sp--
+
+			iterable, ok := (*dst).(objects.Iterable)
+			if !ok {
+				filePos = v.fileSet.Position(v.curFrame.fn.SourceMap[v.ip])
+				err = fmt.Errorf("not iterable: %s", (*dst).TypeName())
+				break mainloop
+			}
+
+			iterator = iterable.Iterate()
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &iterator
+			v.sp++
+
+		case compiler.OpIteratorNext:
+			iterator := v.stack[v.sp-1]
+			v.sp--
+
+			hasMore := (*iterator).(objects.Iterator).Next()
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			if hasMore {
+				v.stack[v.sp] = truePtr
+			} else {
+				v.stack[v.sp] = falsePtr
+			}
+			v.sp++
+
+		case compiler.OpIteratorKey:
+			iterator := v.stack[v.sp-1]
+			v.sp--
+
+			val := (*iterator).(objects.Iterator).Key()
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &val
+			v.sp++
+
+		case compiler.OpIteratorValue:
+			iterator := v.stack[v.sp-1]
+			v.sp--
+
+			val := (*iterator).(objects.Iterator).Value()
+
+			if v.sp >= StackSize {
+				err = ErrStackOverflow
+				break mainloop
+			}
+
+			v.stack[v.sp] = &val
+			v.sp++
+
+		default:
+			panic(fmt.Errorf("unknown opcode: %d", v.curInsts[v.ip]))
+		}
+	}
+
+	if err != nil {
+		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.SourceMap[v.curFrame.ip-1])
+			err = fmt.Errorf("%s\n\tat %s", err.Error(), filePos)
+		}
+		return err
+	}
+
+	// check if stack still has some objects left
+	if v.sp > 0 && atomic.LoadInt64(&v.aborting) == 0 {
+		panic(fmt.Errorf("non empty stack after execution: %d", v.sp))
+	}
+
+	return nil
+}
+
+// Globals returns the global variables.
+func (v *VM) Globals() []*objects.Object {
+	return v.globals
+}
+
+func indexAssign(dst, src *objects.Object, selectors []*objects.Object) error {
+	numSel := len(selectors)
+
+	for sidx := numSel - 1; sidx > 0; sidx-- {
+		indexable, ok := (*dst).(objects.Indexable)
+		if !ok {
+			return fmt.Errorf("not indexable: %s", (*dst).TypeName())
+		}
+
+		next, err := indexable.IndexGet(*selectors[sidx])
+		if err != nil {
+			if err == objects.ErrInvalidIndexType {
+				return fmt.Errorf("invalid index type: %s", (*selectors[sidx]).TypeName())
+			}
+
+			return err
+		}
+
+		dst = &next
+	}
+
+	indexAssignable, ok := (*dst).(objects.IndexAssignable)
+	if !ok {
+		return fmt.Errorf("not index-assignable: %s", (*dst).TypeName())
+	}
+
+	if err := indexAssignable.IndexSet(*selectors[0], *src); err != nil {
+		if err == objects.ErrInvalidIndexValueType {
+			return fmt.Errorf("invaid index value type: %s", (*src).TypeName())
+		}
+
+		return err
+	}
+
+	return nil
+}
+
+func init() {
+	builtinFuncs = make([]objects.Object, len(objects.Builtins))
+	for i, b := range objects.Builtins {
+		builtinFuncs[i] = &objects.BuiltinFunction{
+			Name:  b.Name,
+			Value: b.Func,
+		}
+	}
+}