let function

Brendan Eich brendan at mozilla.org
Tue May 19 20:03:18 UTC 2015

C. Scott Ananian wrote:
> On Tue, May 19, 2015 at 12:24 PM, Steve Fink <sphink at gmail.com 
> <mailto:sphink at gmail.com>> wrote:
>     That visually collides with destructuring for me.
>     let [a, b] = foo();
>     let {a, b} = foo();
>     let f(a, b) = foo(); # Very different
>     I almost expect that last one to use f as a custom matcher of some
>     sort, given the previous two.
> Well *there's* an interesting proposal.  As I understand it, this 
> corner of the grammar is free, so custom matchers would be a 
> possibility here.
> I can imagine some interesting uses for custom data types, eg:
> let pair(a, b) = foo(); // like `let {head, tail} = foo();` but with 
> custom type checking.
> let polar(radius, angle) = point(1, 2); // custom matcher can convert 
> between coordinate respresentations
> or even build a simple matching case statement for a recursive decent 
> parser:
> let for_statement(init, cond, incr) = input_text;
> Does that spark ideas in anyone else?

Sure, and we've had pattern matching on the agenda for a while (distinct 
from destructuring in ES6: refutable match, richer pattern language).

(arossberg: anything newer on github?)
http://wiki.ecmascript.org/doku.php?id=strawman:pattern_matching (older 
strawman from dherman)

I agree that `let f(x) = y` encroaches confusingly on pattern matching, 
not let-function declaration.


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