return when desugaring to closures
brendan at mozilla.com
Mon Oct 13 17:09:48 PDT 2008
On Oct 13, 2008, at 5:00 PM, Jon Zeppieri wrote:
> On Mon, Oct 13, 2008 at 7:39 PM, Brendan Eich <brendan at mozilla.com>
>> On Oct 13, 2008, at 4:14 PM, Jon Zeppieri wrote:
>>> Yes, and binding a fresh induction variable on every iteration makes
>>> sense for a 'for-each' loop (as in the bug report you cited), where
>>> the user is not in charge of updating the induction variable by
>>> of explicit assignment. In a plain 'for' loop, however, it *is*
>>> if an assignment results in a fresh binding.
>> Why is the assignment operator relevant? The question is the binding
>> scope of i in
>> for (let i = 0; i < N; i++) ...
> How is scope the issue? As far as I know, we don't disagree about
Probably we're at cross purposes (I often am ;-) because of the primal
sin in ECMAScript of specifying scope via object, and closure via
scope chain capture.
> The assignment I'm referring to, in this example, is the 'i++' part.
> Mark is proposing that this does not mean "increment i by one," but
> rather "rebind i with the value of i+1" -- which is completely
> different and not what the user wrote.
Gotcha -- I agree, this is a problem for a proposal that tries to
desugar for(;;). Curses.
The user expectation with a closure in a for(var i = 0; i < N; i++)
loop, that each closure captures i's current value, remains,
completely parallel to the for (i in o) ... case. Any attempt to solve
it via let instead of var -- other than by making multiple (blech)
scope (barf) objects, one per iteration -- must respecify how closures
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