I think since we can only break/continue to labels in a linear chain
upwards, break could take a number for how many loops it should break.
This could still be tested at compile time as well, but would lead to
somewhat less readable code. It would however be incompatible with
current label based breaks (easier to find an replace if a compiler
warns you).
while(true) {
while(true) {
break 2;
}
}
Anywho, I don't personally like number based breaking, just throwing
around ideas.
Cheers,
Bradley
On Sat, Apr 9, 2011 at 4:10 AM, Claus Reinke <claus.rei...@talk21.com> wrote:
>> Can we remove labels from the next version of the spec?
>
> I'm not a fan of labels, at least not as a built-in language
> construct - I'd much prefer if the language was expressive enough to emulate
> such functionality when needed (that
> includes useable syntax), not to mention reducing the
> need for such features in the first place.
> However, as long as Javascript has break and continue, ..
>
>> Am I missing anything? Or are there cases where labels allow you do
>> something that's impossible without labels?
>
> It seems that language features like lambdas have been shot
> down because of their interaction with break and continue.
> In brief, people want to be able to abstract over syntax phrases
> like the one marked with -| .. |- here, by wrapping it in some
> form of immediately called function and still have it behave as before:
>
> while (..) { .. -| break; |- .. }
>
> [aside: as far as I understand Tennent, this has nothing to do
> with his principles of correspondence or abstraction, which
> are often misquoted and conjured with in the archives]
>
> Now, if we want to wrap that phrase into a function (not a
> syntax macro), then that function cuts through the while/break
> construct. Still, we can refactor the code a little to make that
> wrapping possible:
>
> loop: while (..) { .. switch ( -| function() { return 'break'; } ()
> |- ) {
> case 'break' : break loop;
> case 'continue' : continue loop;
> }
> .. }
>
> With this change, we are able to wrap code involving break
> or continue into a function (and move that function definition
> out of the loop body). Since the switch statement has its own
> break-target, we need the loop label, even though the original
> break did not have a label.
>
> There are other ways to handle this situation, but this seemed
> to be the most direct way of expressing the intention, given that labels are
> not first-class values in Javascript.
>
> Better alternatives welcome,
> Claus
>
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>
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