SOURCE

function InputStream(input) {
  var pos = 0;
  var line = 1;
  var col = 0;
  function next() {
    var ch = input.charAt(pos++);
    if (ch === '\n') {
      line++;
      col = 0;
    } else {
      col++;
    }
    return ch;
  }

  function peek() {
    return input.charAt(pos);
  }

  function eof() {
    return peek() === '';
  }

  function croak(msg) {
    throw new Error(msg + '(' + line + ':' + col + ')');
  }

  return {
    next: next,
    peek: peek,
    eof: eof,
    croak: croak
  };
}

function TokenStream(input) {
  var current = null;
  var keywords = ' if then else lambda λ true false ';

  function next() {
    var tok = current;
    current = null;
    return tok || read_next();
  }

  function eof() {
    return peek() === null;
  }

  function peek() {
    return current || (current = read_next());
  }

  function read_while(fn) {
    var str = '';
    while (!input.eof() && fn(input.peek())) {
      str += input.next();
    }
    return str;
  }

  function is_whitespace(ch) {
    return ' \t\n'.indexOf(ch) > -1;
  }

  function is_digit(ch) {
    return /[0-9]/i.test(ch);
  }

  function is_op_char(ch) {
    return "+-*/%=&|<>!".indexOf(ch) >= 0;
  }

  function is_keyword(x) {
    return keywords.indexOf(' ' + x + ' ') > -1;
  }

  function is_id_start(ch) {
    return /[a-zλ_]/i.test(ch);
  }

  function is_id(ch) {
    return is_id_start(ch) || "?!-<>=0123456789".indexOf(ch) >= 0;
  }

  function is_punc(ch) {
    return ",;(){}[]".indexOf(ch) >= 0;
  }

  function read_ident() {
    var id = read_while(is_id);
    return {
      type: is_keyword(id) ? "kw": "var",
      value: id
    };
  }

  function read_number() {
    var has_dot = false;
    var number = read_while(function(ch) {
      if (ch == ".") {
        if (has_dot) return false;
        has_dot = true;
        return true;
      }
      return is_digit(ch);
    });
    return {
      type: "num",
      value: parseFloat(number)
    };
  }

  function read_escaped(end) {
    var escaped = false,
    str = "";
    input.next();
    while (!input.eof()) {
      var ch = input.next();
      if (escaped) {
        str += ch;
        escaped = false;
      } else if (ch == "\\") {
        escaped = true;
      } else if (ch == end) {
        break;
      } else {
        str += ch;
      }
    }
    return str;
  }

  function read_next() {
    read_while(is_whitespace);
    if (input.eof()) {
      return null;
    }
  }

  function read_string() {
    return {
      type: "str",
      value: read_escaped('"')
    };
  }

  function skip_comment() {
    read_while(function(ch) {
      return ch != "\n"
    });
    input.next();
  }

  function read_next() {
    read_while(is_whitespace);
    if (input.eof()) return null;
    var ch = input.peek();
    if (ch == "#") {
      skip_comment();
      return read_next();
    }
    if (ch == '"') return read_string();
    if (is_digit(ch)) return read_number();
    if (is_id_start(ch)) return read_ident();
    if (is_punc(ch)) return {
      type: "punc",
      value: input.next()
    };
    if (is_op_char(ch)) return {
      type: "op",
      value: read_while(is_op_char)
    };
    input.croak("Can't handle character: " + ch);
  }

  return {
    next: next,
    peek: peek,
    eof: eof,
    croak: input.croak
  }
}

function parse() {
  var PRECEDENCE = {
    '=': 1,
    '||': 2,
    '&&': 3,
    '<': 7,
    '>': 7,
    ''
  }
}