Support AGen specification for asynchronous generators

[CrabDude]

To generate discussion, feedback and achieve interoperability:

@Raynos and I put together the AGen specification with feedback from @creationix for asynchronous generators, generators + asynchrony (e.g., promises, continuables, etc...) which we're using in our own libraries (gens) to create a cohesive specification for asynchronous generator interoperability.

Some highlights:

• Asynchrony agnostic: implementor/user could support promises, thunks, or something new and exotic, but must support yielding on generator objects.
• Support for serial (vanilla yield) or parallel (yield [...]) execution.
• Separation of Errors and Exceptions

[Raynos]

Right now the AGen spec has some thought into it to handle the majority of the common use cases without external helper libraries.

If we can get some minimal interop between generator runner libraries you can start exporting generator functions on npm and use yield* functionFromOtherModule().

Feedback is welcome on what a good minimal set of runner functionality is so that generator functions exported by modules can work with multiple runners

[tj]

cool ill try and take a look at the spec soon, the end-goal is to delegate the use of a backing lib to the app? sounds reasonable to me, it's a little unfortunate that we'd have to end up using yield * everywhere haha, but I guess that's as good as we get with javascript

[jonathanong]

closing for now since it's so vague. reopen if you have specifics.

honestly, i don't think people should be writing stuff with generators. return promises =/