Ok, final and most delicate part of the mission here: allow (v) -> {k: v} and
even -> {} to return objects, not make useless block statements.
// Expression bodies needs no parentheses or braces
let identity = (x) -> x;
// Fix: object initialiser need not be parenthesized, see Grammar Changes
let key_maker = (val) -> {key: val};
Thanks to Doug for pushing on this idea. I believe that it is sound (still to
be formalized and tested mechanically) in a bottom-up parser.
The top-down approach by default is to parse a cover grammar until an
unambiguous decision point is reached, then depending on the decision, rewrite
the AST (e.g., to make a labeled statement in a block instead of an object
initializer).
/be
On May 15, 2011, at 10:26 AM, Brendan Eich wrote:
> On May 14, 2011, at 11:33 PM, Brendan Eich wrote:
>
>> Grammar Changes
To enable unparenthesized ObjectLiteral expressions as bodies of arrow
functions, without ambiguity with Block bodies, restrict LabelledStatement as
follows:
LabelledStatement :
Identifier : LabelledStatement
Identifier : LabelUsingStatement
LabelUsingStatement :
NonEmptyBlock
IfStatement
IterationStatement
BreakStatement
SwitchStatement
TryStatement
NonEmptyBlock : // See 12.1
{ StatementList }
The resulting grammar should be unambiguously LR(1) (ignoring ASI), because {
L: expr...} can parse only as an ObjectLiteral, and { L: { if (cond)... } } or
similar LabelUsingStatement variations can parse only as a LabelledStatement.
TODO: evaluate top-down parsing difficulty_______________________________________________
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