It's a lisp in js.

gistfile1.js

Array.prototype.map = function(func) {
    var ret = [];
    for (var i = 0; i < this.length; i++)
    ret[i] = func(this[i]);
    return ret;
}

var lisp = function() {
    var builtin = {
        cns: function(args) {
            return [eval(args[0]), eval(args[1])];
        },
        car: function(args) {
            return eval(args[0])[0];
        },
        cdr: function(args) {
            return eval(args[0])[1];
        },
        quo: function(args) {
            return args[0];
        },
        eq: function(args) {
            return eval(args[0]) === eval(args[1]);
        },
        cnd: function(args) {
            if (eval(args[0])) return eval(args[1]);
            return eval(args[2]);
        },
        fun: function(args) {
            return {
                fun: true,
                args: args[0],
                code: args.slice(1, args.length)
            };
        }
    };

    var names = [{}];

    var eval = function(ast) {
        var f, args, i, ret;

        if (!Array.isArray(ast) || ast.length === 0) return names[0][ast] || ast;

        f = ast.shift();
        f = Array.isArray(f) ? eval(f) : f;
        if (builtin.hasOwnProperty(f)) return builtin[f](ast);

        if (f.fun) {
            n = {}
            args = ast.map(eval);
            for (i = 0; i < f.args.length; i++)
            n[f.args[i]] = eval(args[i]);
            names.unshift(n);
            ret = f.code.map(eval).pop();
            names.shift();
            return ret;
        }
    }
    return eval;
}();

lisp(["car", [["fun", ["a"], ["cns", "a", ["quo", "c"]]], ["quo", "d"]]])==="d";​