yaegi

Yaegi is Another Elegant Go Interpreter. It powers executable Go scripts and plugins, in embedded interpreters or interactive shells, on top of the Go runtime.

Features

  • Complete support of Go specification
  • Written in pure Go, using only the standard library
  • Simple interpreter API: New(), Eval(), Use()
  • Works everywhere Go works
  • All Go & runtime resources accessible from script (with control)
  • Security: unsafe and syscall packages not used or exported by default
  • Support Go 1.11 and Go 1.12 (the latest 2 major releases)

Install

As library

import "github.com/containous/yaegi/interp"

REPL

go get -u github.com/containous/yaegi/cmd/yaegi

Note that you can use rlwrap (install with your favorite package manager),
and alias the yaegi command in alias yaegi='rlwrap yaegi' in your ~/.bashrc, to have history and command line edition.

Usage

As an embedded interpreter

Create an interpreter with New(), run Go code with Eval():

package main

import (
	"github.com/containous/yaegi/interp"
	"github.com/containous/yaegi/stdlib"
)

func main() {
	i := interp.New(interp.Options{})

	i.Use(stdlib.Symbols)

	_, err := i.Eval(`import "fmt"`)
	if err != nil {
		panic(err)
	}

	_, err = i.Eval(`fmt.Println("Hello Yaegi")`)
	if err != nil {
		panic(err)
	}
}

Go Playground

As a dynamic extension framework

The following program is compiled ahead of time, except bar() which is interpreted, with the following steps:

  1. use of i.Eval(src) to evaluate the script in the context of interpreter
  2. use of v, err := i.Eval("foo.Bar") to get the symbol from the interpreter context, as a reflect.Value
  3. application of Interface() method and type assertion to convert v into bar, as if it was compiled
package main

import "github.com/containous/yaegi/interp"

const src = `package foo
func Bar(s string) string { return s + "-Foo" }`

func main() {
	i := interp.New(interp.Options{})

	_, err := i.Eval(src)
	if err != nil {
		panic(err)
	}

	v, err := i.Eval("foo.Bar")
	if err != nil {
		panic(err)
	}

	bar := v.Interface().(func(string) string)

	r := bar("Kung")
	println(r)
}

Go Playground

As a command line interpreter

The Yaegi command can run an interactive Read-Eval-Print-Loop:

$ yaegi
> 1 + 2
3
> import "fmt"
> fmt.Println("Hello World")
Hello World
>

Or interpret Go files:

$ yaegi cmd/yaegi/yaegi.go
>

GitHub