On May 23, 2011, at 6:51 PM, Brendan Eich wrote:
> Done, at http://wiki.ecmascript.org/doku.php?id=strawman:block_lambda_revival
> -- this was easy, but it made me wonder whether parentheses for the plain
> Expression arguments that may occur after the leading BlockLambda ought not
> better be curly braces. IOW, instead of
>
> bar = foo {|x| x * x} (42);
>
> support this:
>
> bar = foo {|x| x * x} {42};
>
> This is more uniform on its own new terms. If the first actual parameter
> wants to be an expression, the programmer must parenthesize the entire
> argument list (comma separated of course), or else write {| | 42} as the
> first argument.
>
> So, are curlies better than parens in this situation? I think it is a bit of
> a corner case, but good to address to avoid the currying hazard.
Silly of me, tempted by syntactic prettiness but this idea does nothing to
address your objection.
But here is a grammar change, not too big (and required for yield expressions
anyway) that does help:
[from
http://wiki.ecmascript.org/doku.php?id=strawman:arrow_function_syntax#grammar_changes]
Change all uses of AssignmentExpression outside of the Expression sub-grammar
to InitialValue:
ElementList : // See 11.1.4
Elisionopt InitialValue
ElementList , Elisionopt InitialValue
...
PropertyAssignment : // See 11.1.5
PropertyName : InitialValue
...
ArgumentList : // See 11.2
InitialValue
ArgumentList , InitialValue
...
Initialiser : // See 12.2
= InitialValue
InitialiserNoIn : // See 12.2
= InitialValueNoIn
Define InitialValue:
InitialValue :
AssignmentExpression
CallWithBlockArguments
Define CallWithBlockArguments:
CallWithBlockArguments :
CallExpression BlockArguments
extend PrimaryExpression:
PrimaryExpression :
...
( CallWithBlockArguments )
And BlockArguments as follows:
BlockArguments :
BlockLambda
BlockArguments [no LineTerminator here] BlockLambda
BlockArguments [no LineTerminator here] ( Expression )
The InitialValue non-terminal will also produce YieldExpression for generators,
already in Harmony.
This is not nearly so bad as "significant surgery of nearly the entire
expression stack in the grammar", but I may be missing something.
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