Just as a heads up, something semantically identical to this is what prompted this big shutdown from Mark Miller, and is why the bar raised pretty high since for new features:
https://esdiscuss.org/topic/the-tragedy-of-the-common-lisp-or-why-large-languages-explode-was-revive-let-blocks On Tue, Aug 21, 2018 at 12:20 Herbert Vojčík <[email protected]> wrote: > Hi! > > It would be nice to know if do expressions have some a chance, otherwise > some other syntax for let-in would be really helpful, especially now > that we have arrow functions. > > I would propose to use different variant of let (maybe also const): > > OP 1: > > let in a = b(), if (a) a.c(); > > OP 2: > > let in a = b(), if (a) c(a); > > Instead of > const big = raw => { > let cooked = cook(raw); > return consumer => { > // do things with consumer and cooked > }; > }; > > const big = raw => > let in cooked = cook(raw), consume => { > // do things with consumer and cooked > }; > > In short, > > let in binding = expr, stmt|expr > > It may work for `const in` as well. > > Herby > > P.S.: Alternative syntax is "let a=3, b=4, ..., in foo(a,b,c,d)" but > this can only tell late if it is plain let-up-to-end-of-scope or > local-scope-let, so not sure if that may be a problem; OTOH you can > chain more of them and resembles classical let-in better. > > Isiah Meadows wrote on 21. 8. 2018 20:17: > > It's possible, but the ability to optionally destructure is what would > > make this feature worth it - I feel this should wait for pattern > > matching to be added first, though. > > > > On Tue, Aug 21, 2018 at 11:10 Jordan Harband <[email protected] > > <mailto:[email protected]>> wrote: > > > > ``` > > { > > let a = b(); > > if (a) { > > c(a); > > } > > } > > ``` > > > > On Tue, Aug 21, 2018 at 10:54 AM, Ali Rahbari <[email protected] > > <mailto:[email protected]>> wrote: > > > > while it's possible to use let keyword in for loop parentheses, > > it's not possible to use it in if parentheses. > > > > There are two use cases for this: > > > > *1- if (let a = b()) a.c();* > > this can be done using optional chaining which is proposed: > > b()?.c(); > > > > *2- if (let a = b()) c(a);* > > this or more sophisticated patterns can't be done in any way > > other than this: > > let a = b(); > > if (a) c(a); > > > > the problem here beside more line of codes, is *a *is defined > > outside of if scope. > > > > > > _______________________________________________ > > es-discuss mailing list > > [email protected] <mailto:[email protected]> > > https://mail.mozilla.org/listinfo/es-discuss > > > > > > _______________________________________________ > > es-discuss mailing list > > [email protected] <mailto:[email protected]> > > https://mail.mozilla.org/listinfo/es-discuss > > > > _______________________________________________ > > es-discuss mailing list > > [email protected] > > https://mail.mozilla.org/listinfo/es-discuss > > >
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