Tengo is an embeddable script language for Go.
Tengo is fast as it's compiled to bytecode and executed on stack-based VM that's written in native Go.
>> Try Tengo Playground <<
- Simple and intuitive syntax
- Dynamically typed with type coercions
- 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)
- Executable as a standalone language (without writing any Go code)
fib(35) | fibt(35) | Type | |
---|---|---|---|
Go | 59ms |
4ms |
Go (native) |
Tengo | 4,809ms |
5ms |
VM on Go |
Lua | 1,752ms |
3ms |
Lua (native) |
go-lua | 5,236ms |
5ms |
Lua VM on Go |
GopherLua | 5,558ms |
5ms |
Lua VM on Go |
Python | 3,132ms |
28ms |
Python (native) |
starlark-go | 16,789ms |
5ms |
Python-like Interpreter on Go |
otto | 85,765ms |
22ms |
JS Interpreter on Go |
Anko | 99,235ms |
24ms |
Interpreter on Go |
fib(35) is a function to compute 35th Fibonacci number, and, fibt(35) is the tail-call version of the same function. You can see all the code used for this test in tengobench.
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 := 'δΉ' // 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.
}
a == "foo" // still "foo"
Type is not directly 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'
See Variable Types for more details on the variable types.
You can use the dot selector (.
) and indexer ([]
) operator to read or write elements of arrays, strings, 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, bytes, array), you can use slice operator ([:]
) too.
a := [1, 2, 3, 4, 5][1:3] // == [2, 3]
b := [1, 2, 3, 4, 5][3:] // == [4, 5]
c := [1, 2, 3, 4, 5][:3] // == [1, 2, 3]
d := "hello world"[2:10] // == "llo worl"
In Tengo, functions are first-class citizen, and, it also supports closures, functions that captures variables in outer scopes. In the following example, the function returned from adder
is capturing base
variable.
adder := func(base) {
return func(x) { return base + x } // capturing 'base'
}
add5 := adder(5)
nine := add5(4) // == 9
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
// ...
}
An error object is created using error
function-like keyword. An error can have any types of value and the underlying value of the error can be accessed using .value
selector.
err1 := error("oops") // error with string value
err2 := error(1+2+3) // error with int value
if is_error(err1) { // 'is_error' builtin function
err_val := err1.value // get underlying value
}
You can load other scripts as modules using import
expression.
Main script:
mod1 := import("./mod1") // assuming mod1.tengo file exists in the current directory
// same as 'import("./mod1.tengo")' or 'import("mod1")'
mod1.func1(a) // module function
a += mod1.foo // module variable
//mod1.foo = 5 // error: module variables are read-only
mod1.tengo
file:
func1 := func(x) { print(x) }
foo := 2
Basically, import
expression returns all the global variables defined in the module as a Map-like value. One can access the functions or variables defined in the module using .
selector or ["key"]
indexer, but, module variables are immutable.
Also, you can use import
to load the standard libraries.
math := import("math")
a := math.abs(-19.84) // == 19.84
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.
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 once and execute it multiple times, you can use 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 'c' 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 before compilation using Script.Add()
function. Then a compiled bytecode c
is used to execute the bytecode and get the value of global variables. In this example, the value of global variable a
is read using Compiled.Get()
function.
If you need the custom data types (outside Tengo's primitive types), you can define your own struct
that implements objects.Object
interface (and optionally 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) )
}
As an alternative to using Script, you can directly create and interact with the parser, compiler, and, VMs directly. There's no good documentation yet, but, check out Script code if you are interested.
Although Tengo is designed as an embedded script language for Go, it can be compiled and executed as native binary using tengo
tool.
To install tengo
tool, run:
go get github.com/d5/tengo/cmd/tengo
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`
You can run Tengo REPL if you run tengo
with no arguments.
tengo
Things are experimental, and, the focus is on the core language features, stability, basic interoperability, and the performance optimization.
This will be the first versioned release, and, the main goal for v1 is to make Tengo as a fast embeddable script language for Go, which means Tengo will be comparable to other Go-based script languages such as Starlark, Lua VMs, and other interpreters.
- Interoperability with Go code
- Sandbox environment
- More language features such as bound methods and switch-case statements
- Language-level concurrency support
- Tengo Standard Libraries
- Native executables compilation
- More language features