Hey Philip,
you can see
https://esdiscuss.org/topic/proposal-generator-clone-and-generator-goto for
more about this topic.
On Wed, Feb 18, 2015 at 2:02 PM, Philip Polkovnikov <
polkovnikov...@gmail.com> wrote:
> - 1. Where is the function `run`?
>
> The function `run` is pretty classic variation on the code you would see
> in `Q` or `bluebird`.
>
> function run(gen) {
> return function (/* args */) {
> var args = Array.prototype.slice.call(arguments);
> var iter = gen.apply(args);
> (function step(arr) {
> arr.forEach(function (item) {
> iter.copy().next(item);
> });
> })(iter.next());
> };
> }
>
> Probably, it would be nice to work out `return` there, so that this could
> be a full-fledged nondeterminism monad, but everything should be already
> clear.
>
> - 2. I am against copying a generator instance. It's just like cloning a
> context, with many difficulties and ambiguity. Shall we deep-clone or not?
> How to efficiently implement such a method? I don't see useful cases in
> which we need to clone a generator instance.
>
> Regarding the availability of `.copy()` you can read in the description of
> one Python package I've just found:
>
> http://www.fiber-space.de/generator_tools/doc/generator_tools.html
>
> - Given how close ES6 is to ship, I think it's too late to make such
> changes to the spec, we will have to live with it. Use Traceur to generate
> state machines from your "yield functions" and use that as a basis in your
> code.
>
> The `copy` is worth the problems of frame copying. Anyway, I understand
> that ES6 won't have `copy` as standard is just to be released, but it
> should be added to JS once.
>
> 2015-02-13 21:35 GMT+03:00 François REMY <francois.remy....@outlook.com>:
>
>> For the record, I proposed this feature before, and it wasn't seen as a
>> good idea, for some reason:
>> https://esdiscuss.org/topic/function-is-not-mandatory#content-47
>>
>> Given how close ES6 is to ship, I think it's too late to make such
>> changes to the spec, we will have to live with it. Use Traceur to generate
>> state machines from your "yield functions" and use that as a basis in your
>> code.
>>
>> Best regards,
>> François
>>
>> _______________________________
>>
>> As pretty everyone already seen, generators are usually used in
>> composition with promises to yield (pun intended) a plain simple linear
>> code. This solution looks very much like monads from Haskell, yet in a
>> better syntax: every a <- b in Haskell is a = yield b in JS, and that aids
>> to get rid of several useless lines of code.
>>
>> Actually, one could easily implement other monads over Haskell, changing
>> the structure of the data passed to `yield`. Generators + promises are
>> almost a Cont monad (continuations). But here's an issue.
>>
>> Let's take a look at the List monad (nondeterminism), specifically how we
>> would use one in JS:
>>
>> function* doesntMatter() {
>> var a = yield [1, 2, 3];
>> var b = yield [1, 2, 3];
>> return a + b;
>> }
>>
>> Now, when we run(doesntMatter)(), we should get [2, 3, 4, 3, 4, 5, 4, 5,
>> 6]. But there's a problem with implementation: we would like to run the
>> rest of the computation for every item in an array passed to `yield`, but
>> we can't! There's no way one could copy the current state of an iterator.
>>
>> The same happens to our original generator + promise usage. We could use
>> the same syntax to work with events (i.e. repetitive callback calls), not
>> just series of nested callbacks, but we don't have that vital iter.copy()
>> method.
>>
>> Obviously, mentioning Haskell in this message was overkill, and that
>> could be a reason for someone to diasgree that we really need such feature.
>> But, as I previously described, it's quite a natural thing that is missing,
>> and it doesn't have too much in common with Haskell.
>>
>> What is the right way to put this thing into discussion/standardization
>> process? What do you think about it?
>>
>
>
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