On Wed, Jun 24, 2015 at 2:17 PM, Brendan Eich <bren...@mozilla.org> wrote:
> Hrm, the meeting notes don't quite capture it ( > https://github.com/tc39/tc39-notes/blob/bf5190257d22d1c700e203b28edc8d85ee3aadcc/es6/2015-05/may-27.md > is one view; my fault for not editing after), but we have discussed passing > function.sent into the sub-generator in the past. Ben Newman first raised > the idea the other year, but we finally all came to see at the last (May) > meeting that there's no good way to do it in general. > > When you write a delegating generator that does nothing else, it's > tempting to want function.sent delegation. But in general the yield* could > want a different first-next param than what was passed down, especially > when the delegator looks like this: > > function *g2(...args) { prolog code here; maybe-return yield* > g(...args); optional epilog here } > > See the discussion from the May meeting, I'll cite it here:""" > > MM: But it's passing something from before when yield * is evaluated. > > DH: I'm beginning to think that this is the wrong path (passing in > function.next via yield *). > > AWB: You could create some kind of wrapper if you wanted to pass in the > first value to the subgenerator. > > MM: Libraries could do this. > > yield * wrap(g,function.next); > > MM: "wrap" returns an iterator which wraps the generator which primes the > subgenerator with the supplied value. > """ > > Does this make sense? Sorry again for sparse notes. > > /be > > > Jason Orendorff wrote: > >> Quick question about function.sent: >> >> As of ES6, there's this parallel between functions and generators: >> >> // how to wrap a function >> // f2 is equivalent to f, if f doesn't use `this`. >> function f(...) { ... } >> function f2(...args) { return f(...args); } >> >> // how to wrap a generator >> // g2 is equivalent to g, if g doesn't use `this`. >> function* g(...) { ... } >> function* g2(...args) { return yield* g(...args); } >> >> That is, λx.f(x) = f, a sort of beta-equivalence rule, and for >> generators, you just need to add `yield*` to get an analogous rule. My >> understanding is that this is one reason we have `yield*`. (Writing a >> wrapping function/generator that also covers `this` is left as an easy >> exercise.) >> >> Given function.sent, is there still a way to "wrap" a generator? >> >> -j >> _______________________________________________ >> es-discuss mailing list >> es-discuss@mozilla.org >> https://mail.mozilla.org/listinfo/es-discuss >> > _______________________________________________ > es-discuss mailing list > es-discuss@mozilla.org > https://mail.mozilla.org/listinfo/es-discuss > -- Cheers, --MarkM
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