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

• 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

* 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

bench_test.go holds the Go benchmarks every change is measured against: recursive and tail calls, loops, closures, arrays, maps and strings, stdlib calls, and compilation. A change must not slow any of them beyond benchstat's noise.

git checkout master && make bench > old.txt
git checkout my-branch && make bench > new.txt
go run golang.org/x/perf/cmd/benchstat@latest old.txt new.txt

make bench BENCH=Fib COUNT=20 runs a subset.

Where (*VM).run lands in the binary can move Fib, FibTailCall, Loop and Closure by a few percent on some machines. A change touches a benchmark's path when it changes any code the benchmark times, such as the VM, an object's methods or the compiler, or the bytecode the compiler emits for the benchmark's script. If a benchmark moves after a change that touches neither, compare the two binaries, and treat the move as noise when only the function's address changed:

git checkout master && go test -c -o old.test .
git checkout my-branch && go test -c -o new.test .
go tool nm -size old.test new.test | grep 'VM).run$'

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"

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