yield* desugaring

Ron Buckton rbuckton at chronicles.org
Mon Apr 29 10:25:21 PDT 2013


Was there consensus on the return value of the various generator methods being { value?, done? } for next/send/throw? Is it needed for close? 

The desugaring for yield* in the face of using { value?, done? } is more likely (without refutable matching or let expressions for the moment):


```js
let a = yield* EXPR;
```

```js
let a;
{
    let g = EXPR;
    let received = void 0, send = true, result = void 0;
    try {
        while (true) {
            let { value, done } = send ? g.send(received) : g.throw(received);
            if (done) {
                result = value;
                break;
            }
            try {
                received = yield value;
                send = true;
            }
            catch (e) {
                received = e;
                send = false;
            }
        }
    } 
    finally {
        try { g.close(); } catch (ignored) { }
    }
    a = result;
}
```

Ron

> -----Original Message-----
> From: es-discuss-bounces at mozilla.org [mailto:es-discuss-
> bounces at mozilla.org] On Behalf Of Brendan Eich
> Sent: Monday, April 29, 2013 9:48 AM
> To: Andy Wingo
> Cc: es-discuss
> Subject: Re: yield* desugaring
> 
> Just a straw-spec device, not proposed for ES6 or 7.
> 
> /be
> 
> Andy Wingo wrote:
> > Hi again,
> >
> > On Mon 29 Apr 2013 17:37, Andy Wingo<wingo at igalia.com>  writes:
> >
> >>    let (g = EXPR) {
> >>      let received = void 0, send = true;
> >>      while (true) {
> >>        let next = send ? g.send(received) : g.throw(received);
> >>        if (next.done)
> >>          break;
> >>        try {
> >>          received = yield next.value;  // ***
> >>          send = true;
> >>        } catch (e) {
> >>          received = e;
> >>          send = false;
> >>        }
> >>      }
> >>      next.value;
> >>    }
> >
> > Beyond the scoping error of "next", this desugaring uses let
> > expressions, which AFAICS are not in the spec and have not been
> > discussed in a few years.  Are they actually still a thing?
> >
> > Andy
> > _______________________________________________
> > es-discuss mailing list
> > es-discuss at mozilla.org
> > https://mail.mozilla.org/listinfo/es-discuss
> >
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