simple_parser.js

function EOF () {}

function State (list) {
  this._pos = 0;
  this._list = Array.prototype.slice.call(list).concat([EOF]);
}

State.prototype.getList = function () {
  return this._list.slice(this._pos);
};

State.prototype.consume = function (i) {
  if (i === -1) {
    throw new Error('parse error');
  }
  this._pos += i;
};

function eof(s) {
  if (s.getList()[0] === EOF) {
    s.consume(1);
    return null;
  } else {
    s.consume(-1);
    return null;
  }
}

function chr(c) {
  return function (s) {
    if (s.getList()[0] === c) {
      s.consume(1);
      return c;
    } else {
      s.consume(-1);
      return null;
    }
  };
}

function join(ps) {
  return function (s) {
    var rs = [];
    for (var i = 0; i < ps.length; ++i) {
      var p = ps[i],
          r = p(s);
      if (r !== null) {
        rs.push(r);
      }
    }
    return rs;
  };
}

(function test () {
  var a = chr('a'),
      b = chr('b');
  var p = join([a, b, a, eof]);
  var ps = new State('aba');
  var r = p(ps);
  console.log(r);
})();