I'd like to suggest another sense in which you may have gone down a bad path:
you're assuming that await is paired with function*, but it could instead be
(like C#) paired with its own async-function syntactic form. Let's say for the
sake of argument that async is just a keyword that takes a function form:
async function sizeOfZombocom() {
let all = await download("http://zombo.com";);
return all.length;
}
Imagine we were designing this with a macro system like sweet.js. The
temptation is for `async` to unhygienically bind `await` to a macro within its
body, but Racket has developed a cleaner mechanism for thinking about paired
forms like this, which they call "syntax parameters" (kind of a confusingly
generic sounding name) [1] [2]. The basic idea is that you bind both `async`
and `await` at the same time, so `await` is always bound, even outside of an
async function, but the two collaborate so that `async` informs `await` of its
syntactic context. So it would look something like this:
Example 1:
import { async, await } from "async";
await 1; // syntax error: await used outside of async function
Example 2:
import { async, await } from "async";
function* sizeOfZombocom() {
let all = await download("http://zombo.com";); // syntax error: await used
outside of async function
return all.length;
}
Example 3:
import { async, await } from "async";
async function sizeOfZombocom() {
let all = await download("http://zombo.com";); // great success
return all.length;
}
This makes your abstraction airtight: `await` is a concept that belongs to
`async` functions, not generator functions; generator functions are merely the
internal implementation technique.
Currently, sweet.js doesn't have syntax parameters, but it'd be a good
experiment to add them them and try implementing async/await as I've sketched
here.
Dave
[1] http://www.greghendershott.com/fear-of-macros/Syntax_parameters.html
[2] http://docs.racket-lang.org/reference/stxparam.html
On Jan 23, 2014, at 2:14 PM, Bradley Meck <[email protected]> wrote:
> I was playing around with generators / looking at await for promises and
> notices a very difficult thing revolving around generators not having a
> reference to themselves.
>
> See:
>
> https://gist.github.com/bmeck/72a0f4f448f20cf00f8c
>
> I have to end up wrapping the generator function to get a reference to the
> generator for passing to nested functions.
>
> Is there a reason the execution context is not a generator / there is no
> reference back to the generator during [[call]]?
> _______________________________________________
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