Golang LISP Interpreter

GLISP is a LISP interpreter I implemented in the Go programming language. It was designed as an embedded extension language for Go. It features a hand-rolled lexer and parser and executes on a simple stack-based virtual machine. The language features Clojure-like syntax, proper tail-call optimization, and an easy-to-use Go API.

The code can be found on Github.

; factorial algorithm implemented in GLISP
; using tail recursion
(defn factorial-loop [n acc]
    (cond (= n 0) acc
        (factorial-loop (- n 1) (* n acc))))
(defn factorial [n]
    (factorial-loop n 1))
package main

import (

// implementing factorial in Go to be used in GLISP

func FactorialFunction(env *glisp.Glisp, name string,
        args []glisp.Sexp) (glisp.Sexp, error) {
    if len(args) != 1 {
        return glisp.SexpNull, glisp.WrongNargs

    res := 1
    var n int
    switch t := args[0].(type) {
    case glisp.SexpInt:
        n = int(t)
        return glisp.SexpNull, errors.New("factorial argument must be integer")

    if n < 0 {
        return glisp.SexpNull, errors.New("factorial argument must be positive")

    for i := 1; i <= n; i++ {
        res *= i

    return glisp.SexpInt(res), nil

// creating glisp environment and calling factorial function

func main() {
    env := glisp.NewGlisp()
    env.AddFunction("factorial", FactorialFunction)
    res, _ := env.EvalString("(factorial 5)")

    switch t := res.(type) {
    case glisp.SexpInt:
        fmt.Printf("result is %d\n", t)