I agree with Dmitry on these points. In short: the new Generator(...) syntax
still requires its argument to be a generator function, so you've just added
pointless extra make-work to create one. And as Dmitry points out, you can
always implement that constructor yourself in JS.
What I think is more important is to have an API that lets you actually test
whether a function (which may have been created somewhere else entirely) is a
generator function. That's why I added an API to the spec:
Function.isGenerator(f)
which returns a boolean indicating whether f is a generator function. See:
http://wiki.ecmascript.org/doku.php?id=strawman:generators#api
JJB: you could use this to make your implementation of a Generator constructor
more robust, e.g.:
function Generator(fn, self, args) {
if (!Function.isGenerator(fn))
throw new TypeError("not a generator function");
this.generatorFunction = fn.apply(self, args);
}
Generator.prototype = { ... }
Dave
On Mar 14, 2011, at 3:28 PM, Dmitry A. Soshnikov wrote:
> Moreover, forgot to mention. Passing the generator function ("g-function" and
> "g-object" for shortness) as an argument for the `Generator` constructor is
> not good for dynamically bound `this` value (notice, that in Python's `self`
> is just a casual variable/argument, which should be passed manually anyway).
>
> I.e. we should have `this` as `foo` in the following example:
>
> let foo = {
> bar: function () {
> yield (this == foo);
> }
> };
>
> let g = new Generator(foo.bar);
> g.next(); // false
>
> However,
>
> let g = foo.bar();
> g.next(); // true
>
> You may of course pass the context object as the second argument (thus,
> providing explicit `self` as in Python):
>
> function Generator(fn, self) {
> return fn.apply(self);
> }
>
> let g = new Generator(foo.bar, foo);
> g.next(); // true
>
> But I don't see a big need in such a wrapper. If the rules are specified,
> there should be no any confusion with using call expression for getting
> g-object, and then use `next` to executed the continuation.
>
> Dmitry.
>
> On 15.03.2011 18:42, Dmitry A. Soshnikov wrote:
>> On 15.03.2011 17:58, John J. Barton wrote:
>>> On 3/14/2011 10:08 PM, Brendan Eich wrote:
>>>> On Mar 14, 2011, at 11:50 PM, John J. Barton wrote:
>>>>
>>>>> On 11:59 AM, Brendan Eich wrote:
>>>>>> However, there's no way for a generator function to return that
>>>>>> instance, because a generator function always implicitly returns a fresh
>>>>>> generator iterator when invoked. It could store |this| in the heap, and
>>>>>> whatever value |this| receives is saved as part of the shallow
>>>>>> continuation capture by the generator.
>>>>>>
>>>>> The implicit return of a fresh generator iterator makes the example
>>>>> confusing.
>>>> It's just like Python.
>>>
>>> and Python is perfect? Even successful features have room for improvement.
>>>
>>
>> Pyhton's and JS's implementation is just a one of. But for those who work
>> with such an implementation, there should be no a big confusion. Lua in
>> contrast e.g. uses a special `coroutine.create(generatorFn)`
>> (http://lua-users.org/wiki/CoroutinesTutorial) -- similarly to your
>> proposal. But you may do it yourself if it's confusing
>>
>> function Generator(fn) {
>> return fn();
>> }
>>
>> let g = new Generator(function() {
>> yield 1;
>> yield 2;
>> });
>>
>> g.next(); 1
>> g.next(); 2
>>
>> From JS/Python's viewpoint, this may be considered as superficial thing --
>> if you know that the function is a generator function, be prepared that the
>> _call_ creates the generator object. The other call to the same generator
>> function, creates a fresh g-object. And so on. There is no confusion as it
>> would be that the first call create the g-object, and the other calls
>> already yield, no. For yielding `next` method is.
>>
>> P.S.:
>>
>> A small change, e.g. can be to make next as a getter since it doesn't accept
>> arguments.
>>
>> g.next; // 1
>> g.next; // 2
>>
>> But, it's a cosmetic and actually not so needed change.
>>
>> Dmitry.
>>
>>> jjb
>>> _______________________________________________
>>> es-discuss mailing list
>>> [email protected]
>>> https://mail.mozilla.org/listinfo/es-discuss
>>
>
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