On Oct 17, 2008, at 11:05 AM, Waldemar Horwat wrote: > Brendan Eich wrote: >> Is this a perfectly valid for-in statement? >> >> for (a = b in c); >> >> Not according to ES3's grammar. An assignment expression is not >> valid on >> the left of the for-in's "in": >> >> /IterationStatement /*:* >> * ...* >> * for ( */LeftHandSideExpression /*in */Expression /*) */ >> Statement/ >> * for ( var */VariableDeclarationNoIn /*in */Expression /*)
(Note VariableDeclarationNoIn after var.) >> >> */Statement/ >> >> LeftHandSideExpression does not produce an unparenthesized >> AssignmentExpression, and if you parenthesize then PutValue will >> throw >> on the non-Reference result of the assignment, the ReferenceError at >> runtime which again can become SyntaxError at compile time. > > I accidentally took out the "var" in editing the message. It should > have been > > for (var a = ...) > > Waldemar > _ In that case the -NoIn sub-grammar should apply, extended to LetExpressionNoIn. So for (let (a = b) c in d); would do what you want. We would have to change SpiderMonkey for this edge case, but that is our problem (and unlikely to break anyone). /be _______________________________________________ Es-discuss mailing list Es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
