sex_parser.js

function Parser() {
  var that = {}
    , at
    , current
    , tokens;

  function tokenize(source) {
    return source.replace(/\(/g, ' ( ').replace(/\)/g, ' ) ').split(/\s/).filter(function(t){ return t !== ""; });
  }

  function expression() {
    var value;

    if (current === '(') {
      value = [];
      next();

      while (current !== ')') {
        value.push(expression());
      }
      next();
    } else if (isNumber(current)){
      value = number();
    } else if (isBool(current)) {
      value = bool();
    } else {
      value = current;
      next();
    }

    return value;
  }

  function isNumber(token) {
    return !isNaN(+token);
  }

  function number() {
    var value = +current;
    next();
    return value;
  }

  function isBool(token) {
    return token === '#t' || token === '#f';
  }

  function bool() {
    var value;

    if (current === '#t') value = true;
    if (current === '#f') value = false;

    if (value === undefined) throw new Error();

    next();
    return value;
  }

  function next() {
    current = tokens[at];
    at += 1;
    return current;
  }

  that.read = function (source) {
    at = 0;
    current = "";
    tokens = tokenize(source);
    next();

    return expression();
  };

  return that;
}

/*
var p = new Parser();
console.log(p.read('192338'));
console.log(p.read('(def a b)'));
console.log(p.read('(def a (lambda (a) (+ 1 2)))'));
console.log(p.read('(if #t (+ 1 (* 2 3 4 5)))'));
*/