JavaScript Monadic Parser Combinators

parser.js

var bind = function (prev, bridge) {
  return function (input) {
    var result = prev(input);
    return result.length === 0 ? result : bridge(result[0])(result[1]);
  };
};

var result = function (a) {
  return function (input) {
    return [a, input];
  }
};

var failure = function () {
  return function (input) {
    return [];
  };
};

var choice = function (p, q) {
  return function (input) {
    var r = p(input);
    return r.length > 0 ? r : q(input);
  };
};

var item = function () {
  return function (input) {
    return input.length ? [input[0], input.slice(1)] : [];
  };
};

var satisfies = function (predicate) {
  return bind(item(), function (a) {
    return predicate(a) ? result(a) : failure();
  });
};

var many = function (p) {
  return choice(manyOne(p), result([]));
};

var manyOne = function (p) {
  return bind(p, function (x) {
    return bind(many(p), function (xs) {
      return result([x].concat(xs));
    });
  });
};

var character = function (a) {
  return satisfies(function (b) { return a === b; });
};

var string = function (s) {
  if (s === "") return result("");

  return bind( character(s[0]) , function (f) {
    return bind( string( s.slice(1) ), function (fs) {
      return result(f + fs);
    });
  });
};

var regex = function (r) {
  return satisfies(function (a) {
    return r.test(a);
  });
};

var lower = regex(/[a-z]/);
var upper = regex(/[A-Z]/);
var digit = regex(/[0-9]/);