On 20 April 2012 18:18, Brendan Eich <bren...@mozilla.org> wrote: > Patterns can have custom grammar in binding contexts (after let, in catch > heads, etc.), whereas in an assignment expression's left-hand side we'd need > ObjectLiteral and ArrayLiteral to cover the grammar. > > I sense trouble trying to add 'as' to the expression grammar > (AssignmentExpression to be precise). We could parse it and reject it with > supplemental syntax for rvalues, and allow it in lvalues, but there is a > "spec smell". I think from past discussions that TC39 wants the grammar to > be as precise as possible while still LR(1) with lookahead and other > restrictions.
I see, I haven't thought of destructuring assignment. Yes, that's a bit of an annoyance. But IMHO not a big issue either. Honestly, my feeling is that strictly sticking to that principle will overly constrain pattern syntax anyway, if not for 'as' then for the next nice feature. I dimly remember that we had it coming up before. One alternative of course would be to restrict what can occur in an assignment pattern, compared to bindings. The two are quite different semantically, so it could perhaps be argued. But it's not the most pleasant idea either. /Andreas _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
