Le 23/04/2013 01:31, Tab Atkins Jr. a écrit :
> On Mon, Apr 22, 2013 at 2:45 PM, Sam Tobin-Hochstadt <samth at ccs.neu.edu> wrote:
>> What exactly would be the semantic difference between this and just using
>> 'yield'?
> The semantic difference is that 'yield' pauses your execution and
> gives control to the calling code, while 'await' pauses your execution
> and gives control to the promise.  Completely different direction of
> control-passing.
Your description reminds me of coroutines and Dave Herman's article 
about it [1].
Is await immune from the issues described as:
"Once you add coroutines, you never know when someone might call yield 
[considered as a stack pause primitive]. Any function you call has the 
right to pause and resume you whenever they want, even after any number 
of spins of the event loop. Now any time you find yourself modifying 
state, you start worrying that calling a function might interrupt some 
code you intended to be transactional. "

Overall, control-flow related syntax cannot give you authority that goes 
beyond your own frame. If that happens, then any library (think Node.js 
modules which are recursively by hundreds in any decent-sized project, 
so you don't have to to review them all) can start pretend being smart 
and mess with you invariants if you expected the library function to 
return (and that's a very natural thing to expect).

David

[1] 
http://calculist.org/blog/2011/12/14/why-coroutines-wont-work-on-the-web/

Le 23/04/2013 01:31, Tab Atkins Jr. a ?crit :
> On Mon, Apr 22, 2013 at 2:45 PM, Sam Tobin-Hochstadt <samth at ccs.neu.edu> wrote:
>> What exactly would be the semantic difference between this and just using
>> 'yield'?
>
> The semantic difference is that 'yield' pauses your execution and
> gives control to the calling code, while 'await' pauses your execution
> and gives control to the promise.  Completely different direction of
> control-passing.

Your description reminds me of coroutines and Dave Herman's article 
about it [1].
Is await immune from the issues described as:
"Once you add coroutines, you never know when someone might call yield 
[considered as a stack pause primitive]. Any function you call has the 
right to pause and resume you whenever they want, even after any number 
of spins of the event loop. Now any time you find yourself modifying 
state, you start worrying that calling a function might interrupt some 
code you intended to be transactional. "

Overall, control-flow related syntax cannot give you authority that goes 
beyond your own frame. If that happens, then any library (think Node.js 
modules which are recursively by hundreds in any decent-sized project, 
so you don't have to to review them all) can start pretend being smart 
and mess with you invariants if you expected the library function to 
return (and that's a very natural thing to expect).

[1]: http://calculist.org/blog/2011/12/14/why-coroutines-wont-work-on-the-web/