François REMY <mailto:fremycompany_...@yahoo.fr>
January 12, 2012 2:23 PM
Am I wrong if I say there not a bigger issue with block lambda than
with the current object notation on the matter?
Please continue :-).
I mean, does that code mean anything useful?
function() {
{|a,b| a+b};
}
(You need a name for that function if it is a declaration, and from the
context you show, it is.)
Does this perfectly valid JS mean anything useful?
function f() {
(function (a, b) { return a + b; });
}
Nevertheless, it is legal. JS follows C (not Java) in allowing seemingly
useless expression-statements. This can be a source of bugs. It is also
required in some cases, namely when the function expression (in
parentheses) is the completion value of a Program. In such a case that
value could be the wanted result of eval or an eval-like host API.
If not (as it seems to me), it means that a block lambda will not be
used as a statement by itself. If it's the case, it should defined as
an Expression only,
Expression is already a kind of statement, via ExpressionStatement.
Furthermore, an ExpressionStatement *already* cannot start with a left
curly brace. Please read the grammar:
12.4 Expression Statement
Syntax
ExpressionStatement :
[lookahead ? {{, function}] Expression ;
NOTE An ExpressionStatement cannot start with an opening curly brace
because that might make it ambiguous with a Block. Also, an
ExpressionStatement cannot start with the function keyword because that
might make it ambiguous with a FunctionDeclaration.
where there's no anonymous block to conflict the syntax.
This is the conflict you're looking for.
That solution has been chosen for object notation in the past. That way,
function() {
{
(a, b)
a.add(b)
}
}
That is already valid ES1-6.
Others have already replied, but the problem with redefining ( after {
without untenable newline sensitivity is it is a backward-incompatible
change.
/be
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