return when desugaring to closures
brendan at mozilla.com
Fri Oct 17 09:30:08 PDT 2008
On Oct 16, 2008, at 7:04 PM, Waldemar Horwat wrote:
> The parser is required to backtrack until it either finds an
> expansion of the grammar that doesn't generate a syntax error or
> until it discovers that they all do. You can choose to make
> additional syntax errors as per chapter 16, but that does not
> relieve you of the backtracking requirement.
You're right that a bottom up parser will have a reduce-reduce
conflict. For a top-down parser, it's not an issue.
>>> Other examples: What does the following do?
>>> for (a = let (b = c) b in d) ...
>> SyntaxError because no ; after first expression in for (;;) loop
> It can't be a SyntaxError. It's a perfectly valid for-in statement.
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":
for ( LeftHandSideExpression in Expression ) Statement
for ( var VariableDeclarationNoIn in Expression ) 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
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