The Tengo Language

Tengo is a small, dynamic, fast, secure script language for Go.

Tengo is fast and secure because it's compiled/executed as bytecode on stack-based VM that's written in native Go.

/* 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

Features

• Simple and highly readable Syntax
  • Dynamic typing with type coercion
  • Higher-order functions and closures
  • Immutable values
• Securely Embeddable and Extensible
• Compiler/runtime written in native Go (no external deps or cgo)
• Executable as a standalone language / REPL
• Use cases: rules engine, state machine, data pipeline, transpiler

Benchmark

	fib(35)	fibt(35)	Language (Type)
Tengo	2,315ms	3ms	Tengo (VM)
go-lua	4,028ms	3ms	Lua (VM)
GopherLua	4,409ms	3ms	Lua (VM)
goja	5,194ms	4ms	JavaScript (VM)
starlark-go	6,954ms	3ms	Starlark (Interpreter)
gpython	11,324ms	4ms	Python (Interpreter)
Yaegi	11,715ms	10ms	Yaegi (Interpreter)
otto	48,539ms	6ms	JavaScript (Interpreter)
Anko	52,821ms	6ms	Anko (Interpreter)
-	-	-	-
Go	47ms	2ms	Go (Native)
Lua	756ms	2ms	Lua (Native)
Python	1,907ms	14ms	Python2 (Native)

* fib(35): Fibonacci(35)
* fibt(35): tail-call version of Fibonacci(35)
* Go does not read the source code from file, while all other cases do
* See here for commands/codes used

Quick Start

go get github.com/d5/tengo/v2

A simple Go example code that compiles/runs Tengo script code with some input/output values:

package main

import (
	"context"
	"fmt"

	"github.com/d5/tengo/v2"
)

func main() {
	// create a new Script instance
	script := tengo.NewScript([]byte(
`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
})`))

	// 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"
}

Or, if you need to evaluate a simple expression, you can use Eval function instead:

res, err := tengo.Eval(ctx,
	`input ? "success" : "fail"`,
	map[string]interface{}{"input": 1})
if err != nil {
	panic(err)
}
fmt.Println(res) // "success"

References

• Language Syntax
• Object Types
• Runtime Types and Operators
• Builtin Functions
• Interoperability
• Tengo CLI
• Standard Library
• Syntax Highlighters: VSCode, Atom, Vim
• Why the name Tengo? It's from 1Q84.