(function (fn) {
  return function () {
    var gen = fn.apply(this, arguments);

    return new Promise(function (resolve, reject) {
      var callNext = step.bind(null, "next");
      var callThrow = step.bind(null, "throw");

      function step(key, arg) {
        try {
          var info = gen[key](arg);
          var value = info.value;
        } catch (error) {
          reject(error);
          return;
        }

        if (info.done) {
          resolve(value);
        } else {
          Promise.resolve(value).then(callNext, callThrow);
        }
      }

      callNext();
    });
  };
})