function Generator() {}
function GeneratorFunction() {}
function GeneratorFunctionPrototype() {}

// This is a polyfill for %IteratorPrototype% for environments that
// don't natively support it.
var IteratorPrototype = {};
IteratorPrototype[iteratorSymbol] = function () {
  return this;
};

var getProto = Object.getPrototypeOf;
var NativeIteratorPrototype = getProto && getProto(getProto(values([])));
if (NativeIteratorPrototype &&
    NativeIteratorPrototype !== Op &&
    hasOwn.call(NativeIteratorPrototype, iteratorSymbol)) {
  // This environment has a native %IteratorPrototype%; use it instead
  // of the polyfill.
  IteratorPrototype = NativeIteratorPrototype;
}

var Gp = GeneratorFunctionPrototype.prototype = Generator.prototype = Object.create(IteratorPrototype);
GeneratorFunction.prototype = Gp.constructor = GeneratorFunctionPrototype; // < ----------- explodes here