Looks like those restrictions (condition only at the end, only 'for', 'for each', and 'if' clauses) originate in Brendan's original (too-sketchy) proposal, see the "Comprehensions" section of this page:
http://wiki.ecmascript.org/doku.php?id=proposals:iterators_and_generator s IMO we're looking for simple and useful comprehensions for ES4. I think extensions like the ones you are suggesting, though clearly useful, should be prototyped elsewhere before going into the language spec, or at a minimum, be presented in a better developed proposal. --lars > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Jason Orendorff > Sent: 2. april 2008 13:46 > To: Jeff Dyer > Cc: es4-discuss > Subject: Re: grammar update > > On Sun, Mar 30, 2008 at 7:29 PM, Jeff Dyer <[EMAIL PROTECTED]> wrote: > > I've updated the ES4 grammar files linked from > > http://wiki.ecmascript.org/doku.php?id=proposals:normative_grammar > > Thanks for doing this. I noticed that the grammar doesn't allow this: > > [addr > for each (user in users) > if (user.isAdministrator) > for each (addr in user.addresses)] > > Is this intentional? Both Python and Haskell allow the > analogous listcomp. (Oddly enough, if you anti-optimize > this, moving the IfCondition to be after the last > ForInExpression, the proposed ES4 grammar accepts that.) > > Separately, I would appreciate let clauses in ArrayComprehensions: > > [[trial, phi] > for each (trial in trials) > let (phi = hugeExpensiveCalculation(trial)) > if (phi < 1000)] > > Haskell has this feature. I occasionally reach for it in > Python and it isn't there. > > -j > _______________________________________________ > Es4-discuss mailing list > Es4-discuss@mozilla.org > https://mail.mozilla.org/listinfo/es4-discuss > _______________________________________________ Es4-discuss mailing list Es4-discuss@mozilla.org https://mail.mozilla.org/listinfo/es4-discuss
