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

42 files changed, 1205 insertions, 0 deletions

diff --git a/vendor/github.com/d5/tengo/compiler/ast/array_lit.go b/vendor/github.com/d5/tengo/compiler/ast/array_lit.go
new file mode 100644
index 00000000..9fb4ed67
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/array_lit.go
@@ -0,0 +1,35 @@
+package ast
+
+import (
+	"strings"
+
+	"github.com/d5/tengo/compiler/source"
+)
+
+// ArrayLit represents an array literal.
+type ArrayLit struct {
+	Elements []Expr
+	LBrack   source.Pos
+	RBrack   source.Pos
+}
+
+func (e *ArrayLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ArrayLit) Pos() source.Pos {
+	return e.LBrack
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ArrayLit) End() source.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, ", ") + "]"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/assign_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/assign_stmt.go
new file mode 100644
index 00000000..e129114e
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/assign_stmt.go
@@ -0,0 +1,40 @@
+package ast
+
+import (
+	"strings"
+
+	"github.com/d5/tengo/compiler/source"
+	"github.com/d5/tengo/compiler/token"
+)
+
+// AssignStmt represents an assignment statement.
+type AssignStmt struct {
+	LHS      []Expr
+	RHS      []Expr
+	Token    token.Token
+	TokenPos source.Pos
+}
+
+func (s *AssignStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *AssignStmt) Pos() source.Pos {
+	return s.LHS[0].Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (s *AssignStmt) End() source.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, ", ")
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/ast.go b/vendor/github.com/d5/tengo/compiler/ast/ast.go
new file mode 100644
index 00000000..9fd06728
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/ast.go
@@ -0,0 +1,5 @@
+package ast
+
+const (
+	nullRep = "<null>"
+)
diff --git a/vendor/github.com/d5/tengo/compiler/ast/bad_expr.go b/vendor/github.com/d5/tengo/compiler/ast/bad_expr.go
new file mode 100644
index 00000000..771f26fd
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/bad_expr.go
@@ -0,0 +1,25 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// BadExpr represents a bad expression.
+type BadExpr struct {
+	From source.Pos
+	To   source.Pos
+}
+
+func (e *BadExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *BadExpr) Pos() source.Pos {
+	return e.From
+}
+
+// End returns the position of first character immediately after the node.
+func (e *BadExpr) End() source.Pos {
+	return e.To
+}
+
+func (e *BadExpr) String() string {
+	return "<bad expression>"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/bad_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/bad_stmt.go
new file mode 100644
index 00000000..c2d0ae9a
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/bad_stmt.go
@@ -0,0 +1,25 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// BadStmt represents a bad statement.
+type BadStmt struct {
+	From source.Pos
+	To   source.Pos
+}
+
+func (s *BadStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *BadStmt) Pos() source.Pos {
+	return s.From
+}
+
+// End returns the position of first character immediately after the node.
+func (s *BadStmt) End() source.Pos {
+	return s.To
+}
+
+func (s *BadStmt) String() string {
+	return "<bad statement>"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/binary_expr.go b/vendor/github.com/d5/tengo/compiler/ast/binary_expr.go
new file mode 100644
index 00000000..0cc5bba8
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/binary_expr.go
@@ -0,0 +1,30 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+	"github.com/d5/tengo/compiler/token"
+)
+
+// BinaryExpr represents a binary operator expression.
+type BinaryExpr struct {
+	LHS      Expr
+	RHS      Expr
+	Token    token.Token
+	TokenPos source.Pos
+}
+
+func (e *BinaryExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *BinaryExpr) Pos() source.Pos {
+	return e.LHS.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *BinaryExpr) End() source.Pos {
+	return e.RHS.End()
+}
+
+func (e *BinaryExpr) String() string {
+	return "(" + e.LHS.String() + " " + e.Token.String() + " " + e.RHS.String() + ")"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/block_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/block_stmt.go
new file mode 100644
index 00000000..9bde9fa3
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/block_stmt.go
@@ -0,0 +1,35 @@
+package ast
+
+import (
+	"strings"
+
+	"github.com/d5/tengo/compiler/source"
+)
+
+// BlockStmt represents a block statement.
+type BlockStmt struct {
+	Stmts  []Stmt
+	LBrace source.Pos
+	RBrace source.Pos
+}
+
+func (s *BlockStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *BlockStmt) Pos() source.Pos {
+	return s.LBrace
+}
+
+// End returns the position of first character immediately after the node.
+func (s *BlockStmt) End() source.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, "; ") + "}"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/bool_lit.go b/vendor/github.com/d5/tengo/compiler/ast/bool_lit.go
new file mode 100644
index 00000000..e667a5c8
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/bool_lit.go
@@ -0,0 +1,26 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// BoolLit represents a boolean literal.
+type BoolLit struct {
+	Value    bool
+	ValuePos source.Pos
+	Literal  string
+}
+
+func (e *BoolLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *BoolLit) Pos() source.Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *BoolLit) End() source.Pos {
+	return source.Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *BoolLit) String() string {
+	return e.Literal
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/branch_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/branch_stmt.go
new file mode 100644
index 00000000..f6c7fdea
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/branch_stmt.go
@@ -0,0 +1,38 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+	"github.com/d5/tengo/compiler/token"
+)
+
+// BranchStmt represents a branch statement.
+type BranchStmt struct {
+	Token    token.Token
+	TokenPos source.Pos
+	Label    *Ident
+}
+
+func (s *BranchStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *BranchStmt) Pos() source.Pos {
+	return s.TokenPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *BranchStmt) End() source.Pos {
+	if s.Label != nil {
+		return s.Label.End()
+	}
+
+	return source.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
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/call_expr.go b/vendor/github.com/d5/tengo/compiler/ast/call_expr.go
new file mode 100644
index 00000000..0219d7c9
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/call_expr.go
@@ -0,0 +1,36 @@
+package ast
+
+import (
+	"strings"
+
+	"github.com/d5/tengo/compiler/source"
+)
+
+// CallExpr represents a function call expression.
+type CallExpr struct {
+	Func   Expr
+	LParen source.Pos
+	Args   []Expr
+	RParen source.Pos
+}
+
+func (e *CallExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *CallExpr) Pos() source.Pos {
+	return e.Func.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *CallExpr) End() source.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, ", ") + ")"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/char_lit.go b/vendor/github.com/d5/tengo/compiler/ast/char_lit.go
new file mode 100644
index 00000000..592f8744
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/char_lit.go
@@ -0,0 +1,26 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// CharLit represents a character literal.
+type CharLit struct {
+	Value    rune
+	ValuePos source.Pos
+	Literal  string
+}
+
+func (e *CharLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *CharLit) Pos() source.Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *CharLit) End() source.Pos {
+	return source.Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *CharLit) String() string {
+	return e.Literal
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/cond_expr.go b/vendor/github.com/d5/tengo/compiler/ast/cond_expr.go
new file mode 100644
index 00000000..bb1db849
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/cond_expr.go
@@ -0,0 +1,30 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+)
+
+// CondExpr represents a ternary conditional expression.
+type CondExpr struct {
+	Cond        Expr
+	True        Expr
+	False       Expr
+	QuestionPos source.Pos
+	ColonPos    source.Pos
+}
+
+func (e *CondExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *CondExpr) Pos() source.Pos {
+	return e.Cond.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *CondExpr) End() source.Pos {
+	return e.False.End()
+}
+
+func (e *CondExpr) String() string {
+	return "(" + e.Cond.String() + " ? " + e.True.String() + " : " + e.False.String() + ")"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/empty_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/empty_stmt.go
new file mode 100644
index 00000000..a2ac6ffe
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/empty_stmt.go
@@ -0,0 +1,29 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// EmptyStmt represents an empty statement.
+type EmptyStmt struct {
+	Semicolon source.Pos
+	Implicit  bool
+}
+
+func (s *EmptyStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *EmptyStmt) Pos() source.Pos {
+	return s.Semicolon
+}
+
+// End returns the position of first character immediately after the node.
+func (s *EmptyStmt) End() source.Pos {
+	if s.Implicit {
+		return s.Semicolon
+	}
+
+	return s.Semicolon + 1
+}
+
+func (s *EmptyStmt) String() string {
+	return ";"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/error_expr.go b/vendor/github.com/d5/tengo/compiler/ast/error_expr.go
new file mode 100644
index 00000000..7ce5667e
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/error_expr.go
@@ -0,0 +1,29 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+)
+
+// ErrorExpr represents an error expression
+type ErrorExpr struct {
+	Expr     Expr
+	ErrorPos source.Pos
+	LParen   source.Pos
+	RParen   source.Pos
+}
+
+func (e *ErrorExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ErrorExpr) Pos() source.Pos {
+	return e.ErrorPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ErrorExpr) End() source.Pos {
+	return e.RParen
+}
+
+func (e *ErrorExpr) String() string {
+	return "error(" + e.Expr.String() + ")"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/export_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/export_stmt.go
new file mode 100644
index 00000000..64eb7606
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/export_stmt.go
@@ -0,0 +1,27 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+)
+
+// ExportStmt represents an export statement.
+type ExportStmt struct {
+	ExportPos source.Pos
+	Result    Expr
+}
+
+func (s *ExportStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *ExportStmt) Pos() source.Pos {
+	return s.ExportPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ExportStmt) End() source.Pos {
+	return s.Result.End()
+}
+
+func (s *ExportStmt) String() string {
+	return "export " + s.Result.String()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/expr.go b/vendor/github.com/d5/tengo/compiler/ast/expr.go
new file mode 100644
index 00000000..764bacec
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/expr.go
@@ -0,0 +1,7 @@
+package ast
+
+// Expr represents an expression node in the AST.
+type Expr interface {
+	Node
+	exprNode()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/expr_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/expr_stmt.go
new file mode 100644
index 00000000..095a3ad5
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/expr_stmt.go
@@ -0,0 +1,24 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// 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() source.Pos {
+	return s.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ExprStmt) End() source.Pos {
+	return s.Expr.End()
+}
+
+func (s *ExprStmt) String() string {
+	return s.Expr.String()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/file.go b/vendor/github.com/d5/tengo/compiler/ast/file.go
new file mode 100644
index 00000000..fc18b2d7
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/file.go
@@ -0,0 +1,32 @@
+package ast
+
+import (
+	"strings"
+
+	"github.com/d5/tengo/compiler/source"
+)
+
+// File represents a file unit.
+type File struct {
+	InputFile *source.File
+	Stmts     []Stmt
+}
+
+// Pos returns the position of first character belonging to the node.
+func (n *File) Pos() source.Pos {
+	return source.Pos(n.InputFile.Base)
+}
+
+// End returns the position of first character immediately after the node.
+func (n *File) End() source.Pos {
+	return source.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/compiler/ast/float_lit.go b/vendor/github.com/d5/tengo/compiler/ast/float_lit.go
new file mode 100644
index 00000000..670f744b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/float_lit.go
@@ -0,0 +1,26 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// FloatLit represents a floating point literal.
+type FloatLit struct {
+	Value    float64
+	ValuePos source.Pos
+	Literal  string
+}
+
+func (e *FloatLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *FloatLit) Pos() source.Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *FloatLit) End() source.Pos {
+	return source.Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *FloatLit) String() string {
+	return e.Literal
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/for_in_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/for_in_stmt.go
new file mode 100644
index 00000000..18020b56
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/for_in_stmt.go
@@ -0,0 +1,32 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// ForInStmt represents a for-in statement.
+type ForInStmt struct {
+	ForPos   source.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() source.Pos {
+	return s.ForPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ForInStmt) End() source.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()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/for_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/for_stmt.go
new file mode 100644
index 00000000..4b5a0a17
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/for_stmt.go
@@ -0,0 +1,43 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// ForStmt represents a for statement.
+type ForStmt struct {
+	ForPos source.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() source.Pos {
+	return s.ForPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ForStmt) End() source.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()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/func_lit.go b/vendor/github.com/d5/tengo/compiler/ast/func_lit.go
new file mode 100644
index 00000000..2e90ed2b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/func_lit.go
@@ -0,0 +1,25 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// 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() source.Pos {
+	return e.Type.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *FuncLit) End() source.Pos {
+	return e.Body.End()
+}
+
+func (e *FuncLit) String() string {
+	return "func" + e.Type.Params.String() + " " + e.Body.String()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/func_type.go b/vendor/github.com/d5/tengo/compiler/ast/func_type.go
new file mode 100644
index 00000000..2afaabb1
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/func_type.go
@@ -0,0 +1,25 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// FuncType represents a function type definition.
+type FuncType struct {
+	FuncPos source.Pos
+	Params  *IdentList
+}
+
+func (e *FuncType) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *FuncType) Pos() source.Pos {
+	return e.FuncPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *FuncType) End() source.Pos {
+	return e.Params.End()
+}
+
+func (e *FuncType) String() string {
+	return "func" + e.Params.String()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/ident.go b/vendor/github.com/d5/tengo/compiler/ast/ident.go
new file mode 100644
index 00000000..33b7ff76
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/ident.go
@@ -0,0 +1,29 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// Ident represents an identifier.
+type Ident struct {
+	Name    string
+	NamePos source.Pos
+}
+
+func (e *Ident) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *Ident) Pos() source.Pos {
+	return e.NamePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *Ident) End() source.Pos {
+	return source.Pos(int(e.NamePos) + len(e.Name))
+}
+
+func (e *Ident) String() string {
+	if e != nil {
+		return e.Name
+	}
+
+	return nullRep
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/ident_list.go b/vendor/github.com/d5/tengo/compiler/ast/ident_list.go
new file mode 100644
index 00000000..ee8f7db2
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/ident_list.go
@@ -0,0 +1,58 @@
+package ast
+
+import (
+	"strings"
+
+	"github.com/d5/tengo/compiler/source"
+)
+
+// IdentList represents a list of identifiers.
+type IdentList struct {
+	LParen source.Pos
+	List   []*Ident
+	RParen source.Pos
+}
+
+// Pos returns the position of first character belonging to the node.
+func (n *IdentList) Pos() source.Pos {
+	if n.LParen.IsValid() {
+		return n.LParen
+	}
+
+	if len(n.List) > 0 {
+		return n.List[0].Pos()
+	}
+
+	return source.NoPos
+}
+
+// End returns the position of first character immediately after the node.
+func (n *IdentList) End() source.Pos {
+	if n.RParen.IsValid() {
+		return n.RParen + 1
+	}
+
+	if l := len(n.List); l > 0 {
+		return n.List[l-1].End()
+	}
+
+	return source.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 _, e := range n.List {
+		list = append(list, e.String())
+	}
+
+	return "(" + strings.Join(list, ", ") + ")"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/if_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/if_stmt.go
new file mode 100644
index 00000000..b3d65606
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/if_stmt.go
@@ -0,0 +1,40 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// IfStmt represents an if statement.
+type IfStmt struct {
+	IfPos source.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() source.Pos {
+	return s.IfPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *IfStmt) End() source.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
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/immutable_expr.go b/vendor/github.com/d5/tengo/compiler/ast/immutable_expr.go
new file mode 100644
index 00000000..f9843b50
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/immutable_expr.go
@@ -0,0 +1,29 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+)
+
+// ImmutableExpr represents an immutable expression
+type ImmutableExpr struct {
+	Expr     Expr
+	ErrorPos source.Pos
+	LParen   source.Pos
+	RParen   source.Pos
+}
+
+func (e *ImmutableExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ImmutableExpr) Pos() source.Pos {
+	return e.ErrorPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ImmutableExpr) End() source.Pos {
+	return e.RParen
+}
+
+func (e *ImmutableExpr) String() string {
+	return "immutable(" + e.Expr.String() + ")"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/import_expr.go b/vendor/github.com/d5/tengo/compiler/ast/import_expr.go
new file mode 100644
index 00000000..6eff74a9
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/import_expr.go
@@ -0,0 +1,29 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+	"github.com/d5/tengo/compiler/token"
+)
+
+// ImportExpr represents an import expression
+type ImportExpr struct {
+	ModuleName string
+	Token      token.Token
+	TokenPos   source.Pos
+}
+
+func (e *ImportExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ImportExpr) Pos() source.Pos {
+	return e.TokenPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ImportExpr) End() source.Pos {
+	return source.Pos(int(e.TokenPos) + 10 + len(e.ModuleName)) // import("moduleName")
+}
+
+func (e *ImportExpr) String() string {
+	return `import("` + e.ModuleName + `")"`
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/inc_dec_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/inc_dec_stmt.go
new file mode 100644
index 00000000..e4e7f92c
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/inc_dec_stmt.go
@@ -0,0 +1,29 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+	"github.com/d5/tengo/compiler/token"
+)
+
+// IncDecStmt represents increment or decrement statement.
+type IncDecStmt struct {
+	Expr     Expr
+	Token    token.Token
+	TokenPos source.Pos
+}
+
+func (s *IncDecStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *IncDecStmt) Pos() source.Pos {
+	return s.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (s *IncDecStmt) End() source.Pos {
+	return source.Pos(int(s.TokenPos) + 2)
+}
+
+func (s *IncDecStmt) String() string {
+	return s.Expr.String() + s.Token.String()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/index_expr.go b/vendor/github.com/d5/tengo/compiler/ast/index_expr.go
new file mode 100644
index 00000000..bc0992a3
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/index_expr.go
@@ -0,0 +1,32 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// IndexExpr represents an index expression.
+type IndexExpr struct {
+	Expr   Expr
+	LBrack source.Pos
+	Index  Expr
+	RBrack source.Pos
+}
+
+func (e *IndexExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *IndexExpr) Pos() source.Pos {
+	return e.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *IndexExpr) End() source.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 + "]"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/int_lit.go b/vendor/github.com/d5/tengo/compiler/ast/int_lit.go
new file mode 100644
index 00000000..3e1fd98b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/int_lit.go
@@ -0,0 +1,26 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// IntLit represents an integer literal.
+type IntLit struct {
+	Value    int64
+	ValuePos source.Pos
+	Literal  string
+}
+
+func (e *IntLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *IntLit) Pos() source.Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *IntLit) End() source.Pos {
+	return source.Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *IntLit) String() string {
+	return e.Literal
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/map_element_lit.go b/vendor/github.com/d5/tengo/compiler/ast/map_element_lit.go
new file mode 100644
index 00000000..3d7fca9e
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/map_element_lit.go
@@ -0,0 +1,27 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// MapElementLit represents a map element.
+type MapElementLit struct {
+	Key      string
+	KeyPos   source.Pos
+	ColonPos source.Pos
+	Value    Expr
+}
+
+func (e *MapElementLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *MapElementLit) Pos() source.Pos {
+	return e.KeyPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *MapElementLit) End() source.Pos {
+	return e.Value.End()
+}
+
+func (e *MapElementLit) String() string {
+	return e.Key + ": " + e.Value.String()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/map_lit.go b/vendor/github.com/d5/tengo/compiler/ast/map_lit.go
new file mode 100644
index 00000000..a228224d
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/map_lit.go
@@ -0,0 +1,35 @@
+package ast
+
+import (
+	"strings"
+
+	"github.com/d5/tengo/compiler/source"
+)
+
+// MapLit represents a map literal.
+type MapLit struct {
+	LBrace   source.Pos
+	Elements []*MapElementLit
+	RBrace   source.Pos
+}
+
+func (e *MapLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *MapLit) Pos() source.Pos {
+	return e.LBrace
+}
+
+// End returns the position of first character immediately after the node.
+func (e *MapLit) End() source.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, ", ") + "}"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/node.go b/vendor/github.com/d5/tengo/compiler/ast/node.go
new file mode 100644
index 00000000..44677b47
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/node.go
@@ -0,0 +1,13 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// Node represents a node in the AST.
+type Node interface {
+	// Pos returns the position of first character belonging to the node.
+	Pos() source.Pos
+	// End returns the position of first character immediately after the node.
+	End() source.Pos
+	// String returns a string representation of the node.
+	String() string
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/paren_expr.go b/vendor/github.com/d5/tengo/compiler/ast/paren_expr.go
new file mode 100644
index 00000000..8db4ac02
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/paren_expr.go
@@ -0,0 +1,26 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// ParenExpr represents a parenthesis wrapped expression.
+type ParenExpr struct {
+	Expr   Expr
+	LParen source.Pos
+	RParen source.Pos
+}
+
+func (e *ParenExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *ParenExpr) Pos() source.Pos {
+	return e.LParen
+}
+
+// End returns the position of first character immediately after the node.
+func (e *ParenExpr) End() source.Pos {
+	return e.RParen + 1
+}
+
+func (e *ParenExpr) String() string {
+	return "(" + e.Expr.String() + ")"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/return_stmt.go b/vendor/github.com/d5/tengo/compiler/ast/return_stmt.go
new file mode 100644
index 00000000..592d45b8
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/return_stmt.go
@@ -0,0 +1,35 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+)
+
+// ReturnStmt represents a return statement.
+type ReturnStmt struct {
+	ReturnPos source.Pos
+	Result    Expr
+}
+
+func (s *ReturnStmt) stmtNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (s *ReturnStmt) Pos() source.Pos {
+	return s.ReturnPos
+}
+
+// End returns the position of first character immediately after the node.
+func (s *ReturnStmt) End() source.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/compiler/ast/selector_expr.go b/vendor/github.com/d5/tengo/compiler/ast/selector_expr.go
new file mode 100644
index 00000000..31d2e6d1
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/selector_expr.go
@@ -0,0 +1,25 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// 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() source.Pos {
+	return e.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *SelectorExpr) End() source.Pos {
+	return e.Sel.End()
+}
+
+func (e *SelectorExpr) String() string {
+	return e.Expr.String() + "." + e.Sel.String()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/slice_expr.go b/vendor/github.com/d5/tengo/compiler/ast/slice_expr.go
new file mode 100644
index 00000000..e7e2e05b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/slice_expr.go
@@ -0,0 +1,36 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// SliceExpr represents a slice expression.
+type SliceExpr struct {
+	Expr   Expr
+	LBrack source.Pos
+	Low    Expr
+	High   Expr
+	RBrack source.Pos
+}
+
+func (e *SliceExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *SliceExpr) Pos() source.Pos {
+	return e.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *SliceExpr) End() source.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 + "]"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/stmt.go b/vendor/github.com/d5/tengo/compiler/ast/stmt.go
new file mode 100644
index 00000000..6b26ba88
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/stmt.go
@@ -0,0 +1,7 @@
+package ast
+
+// Stmt represents a statement in the AST.
+type Stmt interface {
+	Node
+	stmtNode()
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/string_lit.go b/vendor/github.com/d5/tengo/compiler/ast/string_lit.go
new file mode 100644
index 00000000..2119d34b
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/string_lit.go
@@ -0,0 +1,26 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// StringLit represents a string literal.
+type StringLit struct {
+	Value    string
+	ValuePos source.Pos
+	Literal  string
+}
+
+func (e *StringLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *StringLit) Pos() source.Pos {
+	return e.ValuePos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *StringLit) End() source.Pos {
+	return source.Pos(int(e.ValuePos) + len(e.Literal))
+}
+
+func (e *StringLit) String() string {
+	return e.Literal
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/unary_expr.go b/vendor/github.com/d5/tengo/compiler/ast/unary_expr.go
new file mode 100644
index 00000000..53236146
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/unary_expr.go
@@ -0,0 +1,29 @@
+package ast
+
+import (
+	"github.com/d5/tengo/compiler/source"
+	"github.com/d5/tengo/compiler/token"
+)
+
+// UnaryExpr represents an unary operator expression.
+type UnaryExpr struct {
+	Expr     Expr
+	Token    token.Token
+	TokenPos source.Pos
+}
+
+func (e *UnaryExpr) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *UnaryExpr) Pos() source.Pos {
+	return e.Expr.Pos()
+}
+
+// End returns the position of first character immediately after the node.
+func (e *UnaryExpr) End() source.Pos {
+	return e.Expr.End()
+}
+
+func (e *UnaryExpr) String() string {
+	return "(" + e.Token.String() + e.Expr.String() + ")"
+}
diff --git a/vendor/github.com/d5/tengo/compiler/ast/undefined_lit.go b/vendor/github.com/d5/tengo/compiler/ast/undefined_lit.go
new file mode 100644
index 00000000..8e51b113
--- /dev/null
+++ b/vendor/github.com/d5/tengo/compiler/ast/undefined_lit.go
@@ -0,0 +1,24 @@
+package ast
+
+import "github.com/d5/tengo/compiler/source"
+
+// UndefinedLit represents an undefined literal.
+type UndefinedLit struct {
+	TokenPos source.Pos
+}
+
+func (e *UndefinedLit) exprNode() {}
+
+// Pos returns the position of first character belonging to the node.
+func (e *UndefinedLit) Pos() source.Pos {
+	return e.TokenPos
+}
+
+// End returns the position of first character immediately after the node.
+func (e *UndefinedLit) End() source.Pos {
+	return e.TokenPos + 9 // len(undefined) == 9
+}
+
+func (e *UndefinedLit) String() string {
+	return "undefined"
+}