scheem_interpreter.js

//Node Code Here
//Add more files in the file editor.
//Run the code, test it and share it.
//app.js is your main file which will execute.
//You can add more files and directories in the file Explorer in the left.
"use strict";
var assert = require('assert');
var evalScheem = function (expr, env) {
    // Numbers evaluate to themselves
    if (typeof expr === 'number') {
        return expr;
    }
    // Strings are variable references
    if (typeof expr === 'string') {
        return env[expr];
    }
    // Look at head of list for operation
    //console.log(expr[0]);
    switch (expr[0]) {
        case '+':
            return evalScheem(expr[1], env) +
                   evalScheem(expr[2], env);
        case 'set!':
            env[expr[1]] = evalScheem(expr[2], env);
            return 0;         
        case 'begin':
            // console.log(expr);
            while (expr[2]) {
                evalScheem(expr[1], env);
                expr = (expr.slice(1))
            }
            return evalScheem(expr[1], env);       
    }
};


/* var prg = ['begin',
            ['define', 'x', 5],
            ['set!', 'x', ['+', 'x', 1]],
            ['+', 2, 'x']];
*/

assert.equal(
    evalScheem(['begin', ['set!', 'x', 5], 
        ['set!', 'x', ['+', 'y', 'x']], 'x'], {x:1, y:2}), 7);
assert.equal(evalScheem(['begin', ['+', 2, 2]], {}), 4);
assert.equal(evalScheem(['begin', 1, 2, 3]), 3)
console.log('all tests passed');