On May 10, 2013, at 11:36 AM, Brendan Eich wrote: > Jason Orendorff wrote: >> On Thu, May 9, 2013 at 11:42 PM, Mike Stay <[email protected] >> <mailto:[email protected]>> wrote: >> >> In Scala, this is desugared into >> expr1.flatMap(x => >> expr2(x).flatMap(y => ... >> exprN(x, y, ...).map(z => >> result(x, y, ..., z) >> ) >> ) >> ) >> >> >> Currently comprehensions use the same protocol as for-of statements, namely >> iterators. I think we definitely want them to use the same protocol. >> >> .map() is appealing, but to work with for-of statements, it would have to >> support break, continue, and early return, either using exceptions (like >> Scala's Breaks) or something new. Part of the appeal of the iterator >> protocol is that it doesn't complicate break/continue/return. > > Agreed. JS ain't Scala. > > Note for Mike Stay, in case it helps a bit (just syntax): we agreed to use > LTR order, so: > > [for (x of expr1) for (y of expr2(x)) result(x, y)] > > > to shorten your example a bit. > >> Separately, for the list: are arrow-functions lexically transparent to super >> and arguments? I hope so! For this kind of desugaring, if nothing else. > > 'super' like 'this' is lexical -- the outer function's same-named keyword > meaning. > > 'arguments' per > http://wiki.ecmascript.org/doku.php?id=harmony:arrow_function_syntax is an > error. Perhaps we should change this to match the keywords. Allen?
Oy yeah, look at that... I don't like these sorts of static semantics restrictions on expression elements. PrimaryExpression does't have the context to make the determination and it's a pain to restrict it at the level of ArrowFunction (although I do something like that for yield). I think this spec. complications reflect a user perspective that it is a nanny restriction. We're basically saying: you might not understand the semantics of arguments within an arrow (whatever we decided it was) so we won't let you use it at all. Personally, I prefer Jason's perspective. Arrows don't have their own arguments object and "arguments" just lexically binds. Allen _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
