On Thu, Apr 29, 2010 at 3:32 PM, Brendan Eich <[email protected]> wrote:
> On Apr 29, 2010, at 3:16 PM, Mark S. Miller wrote: > > On Thu, Apr 29, 2010 at 2:39 PM, Brendan Eich <[email protected]> wrote: > >> Really, methinks you guys protest too much. In particular Mike's "all new >> productions that introduce a new keyword should be restricted" is simply >> wrong for "let". >> > > Btw, regarding "let", ASI, and Dave's recent "let" expression proposal < > http://wiki.ecmascript.org/doku.php?id=strawman:let_expressions>, how > should > > let () { => foo } > (3, 4) > > parse? Is it a function call? > > > As far as I can tell, this is covered by ECMA-262 7.9.2: > > The source > * > * > * a = b + c* > * (d + e).print()* > > is *not *transformed by automatic semicolon insertion, because the > parenthesised expression that begins the second > line can be interpreted as an argument list for a function call: > * > * > * a = b + c(d + e).print()* > Formally, that makes sense. But given that all the other <keyword> ... "{" ... "}" productions, if they occur at the beginning of a statement, end with the "}", I think this reading of the let expression may be confusing. What if we adopt the same (admittedly unpleasant) rule we already have for the "function" keyword: It can't begin an expression statement. If it occurs at the beginning of a statement, it is a statement. If you want a let expression in that position, surround it with parens. In other words, better to be unpleasantly consistent than to be inconsistent. (Please no "small mind hobgoblins" ;).) > In the circumstance that an assignment statement must begin with a left > parenthesis, it is a good idea for the > programmer to provide an explicit semicolon at the end of the preceding > statement rather than to rely on automatic > semicolon insertion. > > > As David-Sarah Hopwood pointed out a while ago, there's no error to > correct. > > I'm assuming here that let () { => foo } will be a PrimaryExpression. The > always-braced body avoids reduce-reduce conflicts Waldemar pointed out in > connection with ES4's unbracketed let expression body. > > /be > > -- Cheers, --MarkM
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