The Tengo Language

Tengo is an embedded script language for Go.

>> Try Tengo in online Playground <<

Features

• Simple and intuitive syntax
• Dynamically typed with type coercions
• Bytecode compiled (see the benchmark results)
• First-class functions and Closures
• Garbage collected (thanks to Go runtime)
• Easily extendible using customizable types
• Written in pure Go (no CGO, no external dependencies)
• Excutable as a standalone language (without writing any Go code)

Benchmark

	fib(35)	fibt(35)	Type
Go	68,713,331	3,264,992	Go (native)
Tengo	6,811,234,411	4,699,512	Go-VM
Lua	1,946,451,017	3,220,991	Lua (native)
go-lua	5,658,423,479	4,247,160	Go-Lua-VM
GopherLua	6,301,424,553	5,194,735	Go-Lua-VM
Python	3,159,870,102	28,512,040	Python (native)
otto	91,616,109,035	13,780,650	Go-JS-Interpreter
Anko	119,395,411,432	22,266,008	Go-Interpreter

*Nanoseconds

fib(35) is a function to calculate 35th Fibonacci number.

fib := func(x) {
	if x == 0 {
		return 0
	} else if x == 1 {
		return 1
	} else {
		return fib(x-1) + fib(x-2)
	}
}
fib(35)

fibt(35) is a tail-call version of fib(35).

fibt := func(x, a, b) {
	if x == 0 {
		return a
	} else if x == 1 {
		return b
	} else {
		return fibt(x-1, b, a+b)
	}
}
fibt(35, 0, 1)

Please see tengobench for more details.

Tengo Syntax in 5 Minutes

Tengo supports line comments (//...) and block comments (/* ... */).

/* 
  multi-line block comments 
*/

a := 5 // line comments

Tengo is a dynamically typed language, and, you can initialize the variables using := operator.

a := 1984 		// int
b := "aomame"		// string
c := -9.22		// float
d := true		// bool
e := '九'		// char
f := [1, false, "foo"]	// array
g := {			// map
    h: 439,
    i: 12.34,
    j: [0, 9, false]
}
k := func(l, m) {	// function
    return l + m
}

After the variable is initialized, it can be re-assigned different value using = operator.

a := 1928		// int
a = "foo"		// string
f := func() {
    a := false		// 'a' is defined in the function scope
    a = [1, 2, 3]	// and thus does not affect 'a' in global scope.
}
print(a) 		// still "foo"

Type is not explicitly specified, but, you can use type coercion functions to convert between types.

s1 := string(1984)  // "1984"
i2 := int("-999")   // -999
f3 := float(-51)    // -51.0
b4 := bool(1)       // true
c5 := char("X")     // 'X'

You can use dot selector (.) and indexer ([]) operator to read or write elemens of arrays or maps.

["one", "two", "three"][1]	// == "two"

m := {
    a: 1,
    b: [2, 3, 4],
    c: func() { return 10 }
}
m.a				// == 1
m["b"][1]			// == 3
m.c()				// == 10
m.x = 5				// add 'x' to map 'm'
m.b[5] = 0			// but this is an error: index out of bounds

For sequence types (string or array), you can use slice operator ([:]) too.

[1, 2, 3, 4, 5][1:3]	// == [2, 3]
[1, 2, 3, 4, 5][3:]	// == [4, 5]
[1, 2, 3, 4, 5][:3]	// == [1, 2, 3]
"hello world"[2:10]	// == "llo worl"

In Tengo, functions are first-class citizen and be treated like any other variables. Tengo also supports closures, functions that captures variables in outer scopes. In the following example, the function that's being returned from adder function is capturing base variable.

adder := func(base) {
    return func(x) { return base + x }	// capturing 'base'
}
add5 := adder(5)
nine := add5(4)		// nine

For flow control, Tengo currently supports if-else, for, for-in statements.

// IF-ELSE
if a < 0 {
    // ...
} else if a == 0 {
    // ...
} else {
    // ...
}

// IF with init statement
if a := 0; a < 10 {
    // ...
} else {
    // ...
}

// FOR
for a:=0; a<10; a++ {
    // ...
}

// FOR condition-only (like WHILE in other languages)
for a < 10 {
    // ...
}

// FOR-IN
for x in [1, 2, 3] {		// array: element
    // ...
}
for i, x in [1, 2, 3] {		// array: index and element
    // ...
} 
for k, v in {k1: 1, k2: 2} {	// map: key and value
    // ...
}

Tengo in Go

To execute Tengo code in your Go codebase, you should use Script. In the simple use cases, all you need is to do is to create a new Script instance and call its Script.Run() function like this:

import "github.com/d5/tengo/script"

var code = `
reduce := func(seq, fn) {
    s := 0
    for x in seq { fn(x, s) }
    return s
}

print(reduce([1, 2, 3], func(x, s) { s += x }))
`

func main() {
    s := script.New([]byte(code))
    if _, err := s.Run(); err != nil {
        panic(err)
    }
}

If you want to compile the source script and execute it multiple times, consider using Script.Compile() function that returns Compiled instance.

import (
	"fmt"

	"github.com/d5/tengo/script"
)

func main() {
	s := script.New([]byte(`a := b + 20`))

	// define variable 'b'
	_ = s.Add("b", 10)

	// compile the source
	c, err := s.Compile()
	if err != nil {
		panic(err)
	}

	// run the compiled bytecode
	// a compiled bytecode can be executed multiple without re-compiling it
	if err := c.Run(); err != nil {
		panic(err)
	}

	// retrieve value of 'a'
	a := c.Get("a")
	fmt.Println(a.Int())
}

In the example above, a variable b is defined by the user using Script.Add() function. Then a compiled bytecode (created by Script.Compile()) is used to execute the code and get the value of global variables, like a in this example.

If you want to use your own data type (outside Tengo's primitive types), you can create your struct that implements objects.Object interface (and objects.Callable if you want to make function-like invokable objects).

import (
	"errors"
	"fmt"

	"github.com/d5/tengo/compiler/token"
	"github.com/d5/tengo/objects"
	"github.com/d5/tengo/script"
)

type Counter struct {
	value int64
}

func (o *Counter) TypeName() string {
	return "counter"
}

func (o *Counter) String() string {
	return fmt.Sprintf("Counter(%d)", o.value)
}

func (o *Counter) BinaryOp(op token.Token, rhs objects.Object) (objects.Object, error) {
	switch rhs := rhs.(type) {
	case *Counter:
		switch op {
		case token.Add:
			return &Counter{value: o.value + rhs.value}, nil
		case token.Sub:
			return &Counter{value: o.value - rhs.value}, nil
		}
	case *objects.Int:
		switch op {
		case token.Add:
			return &Counter{value: o.value + rhs.Value}, nil
		case token.Sub:
			return &Counter{value: o.value - rhs.Value}, nil
		}
	}

	return nil, errors.New("invalid operator")
}

func (o *Counter) IsFalsy() bool {
	return o.value == 0
}

func (o *Counter) Equals(t objects.Object) bool {
	if tc, ok := t.(*Counter); ok {
		return o.value == tc.value
	}

	return false
}

func (o *Counter) Copy() objects.Object {
	return &Counter{value: o.value}
}

func (o *Counter) Call(args ...objects.Object) (objects.Object, error) {
	return &objects.Int{Value: o.value}, nil
}

var code = []byte(`
arr := [1, 2, 3, 4]
for x in arr {
	c1 += x
}
out := c1()`)

func main() {
	s := script.New(code)

	// define variable 'c1'
	_ = s.Add("c1", &Counter{value: 5})

	// compile the source
	c, err := s.Run()
	if err != nil {
		panic(err)
	}

	// retrieve value of 'out'
	out := c.Get("out")
	fmt.Println(out.Int()) // prints "15" ( = 5 + (1 + 2 + 3 + 4) )
}

Alternatively, you can directly create and interact with the parser, compiler and VMs directly. There's no good documentations for them, but, you can look at Script code to see how they work each other.

Tengo Standalone

Although Tengo is designed as an embedded script language for Go, it can be compiled and executed as native binary without any Go code using tengo tool.

Installing Tengo Tool

To install tengo tool, run:

go get github.com/d5/tengo/cmd/tengo

Compiling and Executing Tengo Code

You can directly execute the Tengo source code by running tengo tool with your Tengo source file (*.tengo).

tengo myapp.tengo

Or, you can compile the code into a binary file and execute it later.

tengo -c -o myapp myapp.tengo   # compile 'myapp.tengo' into binary file 'myapp'
tengo myapp                     # execute the compiled binary `myapp`	

Tengo REPL

You can run Tengo REPL if you run tengo with no arguments.

tengo

Roadmap

The next big features planned include:

• Module system (or packages)
• Standard libraries
• Better documentations
• More language constructs such as error handling, object methods, switch-case statements
• Native executables compilation
• Performance improvements
• Syntax highlighter for IDEs