On Tue, Aug 6, 2013 at 8:04 PM, jmar777 <[email protected]> wrote:
> I suppose it's worth pointing out that there's (technically) no ambiguity
> about whether or not a yield expression will result in suspension. It
> will. Period.
>
> Granted, sometimes execution may be resumed synchronously, and sometimes
> from an async context, but I think we're already starting to see some
> patterns that give us some indicators there. Specifically, it's fairly
> obvious that the most common approach for async control-flow with
> generators is going to be with the assistance of some sort of utility
> (e.g., suspend, co, gen-run, galaxy, etc.).
>
> That is, consider the following example:
>
> suspend(function* () {
> var user = yield db.getUser('jmar777');
> })();
>
> So, we now have:
>
> 1) function*
> 2) yield
> 3) an intentional call to something returning a promise (or continuable)
> 4) the whole thing is wrapped in a suspend() call, a library who's sole
> purpose is to help with async interactions
>
> I'll concede on an academic level that the syntax itself is ambiguous (but
> hey, that's JavaScript). However, that's where the ambiguity starts *and*
> ends.
> The async/suspend/resume semantics are pretty abundantly clear.
>
The syntax is _irrefutably_ unambiguous—otherwise it wouldn't even be in
the language; yield is not a reserved word and therefore function*() {...}
must exist to provide a _single_ new, declarative syntactic form to provide
the necessary grammatical context in which the word "yield" may be treated
as a language keyword and not just an identifier. It is the very definition
of the word "unambiguous".
Everything prior to that: +1
Rick
> On Tuesday, August 6, 2013 7:31:04 PM UTC-4, Tim Caswell wrote:
>>
>>
>>
>>
>> On Tue, Aug 6, 2013 at 5:20 PM, Mikeal Rogers <[email protected]>wrote:
>>
>>> I think Tim means that the author of the generator should assume it will
>>> be suspended at any time, not the consumer.
>>>
>>
>> Yes, that's exactly what I mean. No function that you call can suspend
>> you simply by calling it. That danger does not exist in ES6's version of
>> generators.
>>
>>
>>
>>>
>>> On Aug 6, 2013, at 3:17PM, Mark Hahn <[email protected]> wrote:
>>>
>>> > Always assume that you will be suspended any time you have a yield or
>>> yield*
>>>
>>> How do you know any of this you see a function call? Only the function
>>> definition looks different. Tell me which is these will yield ..
>>>
>>> a()
>>> b()
>>> c()
>>>
>>> On Tue, Aug 6, 2013 at 2:54 PM, Tim Caswell <[email protected]> wrote:
>>>
>>>>
>>>>
>>>>
>>>> On Tue, Aug 6, 2013 at 4:47 PM, Mikeal Rogers <[email protected]>wrote:
>>>>
>>>>> It is the *exact same* hazard as the code you posted, I don't think it
>>>>> is any *more* of a hazard at the language level. The difference is that
>>>>> the
>>>>> pattern in the function code below is basically never seen in node.js code
>>>>> and it has been *possible* to write it since node's creation.
>>>>>
>>>>> Could be that nobody will use/clobber closure scope in their
>>>>> generators either, but I'm afraid they will because it will work and
>>>>> operate as expected *most* of the time and, unlike the function example
>>>>> you've posted, it will still fit well when used with what I assume will
>>>>> become a healthy ecosystem of generator consuming libraries.
>>>>>
>>>>> The reason nobody writes this kind of thing in node is that it just
>>>>> won't play well with the rest of the libraries in the ecosystem whereas
>>>>> the
>>>>> hazardous generator example looks like it would fit just as well as a
>>>>> "well
>>>>> written" generator until it hits scale and causes visible bugs.
>>>>>
>>>>> All kinds of bad patterns and bad code are possible in any language.
>>>>> The patterns we adopt to create a healthy ecosystem are what will keep
>>>>> people away from the third rails. Depending on people to have "well
>>>>> written" code, by some definition of "well", is not a good alternative to
>>>>> solidifying and encouraging patterns that make it *difficult* to write
>>>>> hazardous code in the first place.
>>>>>
>>>>> No pattern or feature in JavaScript escapes the potential for abuse
>>>>> and bugs, and nothing that I'm worried about w/ respect to generators is
>>>>> worse or better than language level hazards w/ callbacks, it's just that
>>>>> we've created a set of patterns that *discourage* those hazards in the
>>>>> current ecosystem and I'm failing to see how we do that in this particular
>>>>> case with generators.
>>>>>
>>>>
>>>> I propose a simple rule for all generator code:
>>>>
>>>> - Always assume that you will be suspended any time you have a yield
>>>> or yield* and any shared state may change.
>>>>
>>>> If we educate everyone and focus on that one thing (yield) that will
>>>> cover all hazards around shared state and generators, be it async
>>>> promise/continuable based stuff or sync lazy iterator stuff.
>>>>
>>>> Just like with functions we've learned to look for the "function"
>>>> keyword and guard our state around that point, we need to do the same
>>>> around the "yield" keyword.
>>>>
>>>> Teach people correct principles and trust them to do the right thing.
>>>> We'll be fine.
>>>>
>>>>
>>>>
>>>>>
>>>>> -Mikeal
>>>>>
>>>>> On Aug 6, 2013, at 2:33PM, Tim Caswell <[email protected]> wrote:
>>>>>
>>>>> My question to people on the list is how is this any different than
>>>>> the same hazard with normal function?
>>>>>
>>>>> var sum, i;
>>>>> function reduce(arr) {
>>>>> sum = 0;
>>>>> i = 0;
>>>>> return function () {
>>>>> if (i < arr.length) {
>>>>> sum += arr[i++];
>>>>> return sum;
>>>>> }
>>>>> };
>>>>> }
>>>>>
>>>>>
>>>>>
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