On Jun 30, 2011, at 3:47 PM, Brendan Eich wrote:
>> Statement:
>> UnlabeledStatement
>> LabeledStatement
>>
>> UnlabeledStatement:
>> Block
>> VariableStatement
>> EmptyStatement
>> ExpressionStatement
>> ContinueStatement
>> ReturnStatement
>> LabelUsingStatement
>> DebuggerStatement
>>
>> LabelUsingStatement:
>> IfStatement
>> IterationStatement
>> BreakStatement
>> WithStatement
>> SwitchStatement
>> ThrowStatement
>> TryStatement
I forgot to move Block from UnlabeledStatement to LabelUsingStatement. You can
label a block. It's something people do now for break to label. And with the
revisions below, it does not create any ambiguity.
/be
>>
>> LabeledStatement:
>> Identifier : Statement
>>
>> WellLabeledStatement:
>> Identifier : LabelUsingStatement
>> Identifier : WellLabeledStatement
>>
>> ...
>
>> If I have this right, then we could add a new production:
>>
>> PrimaryExpression:
>> Block
>
> This creates an LR(1) ambiguity, a shift-reduce conflict between shifting : in
>
> WellLabeledStatement : Identifier.: LabelUsingStatement
> WellLabeledStatement : Identiifer.: WellLabeledStatement
>
> and reducing on : lookahead via
>
> PropertyName : Identifier.
>
> under PropertyAssignment under ObjectLiteral.
>
> (The dots in the productions are yacc/bison-style cursors showing where the
> parse is.)
>
> One easy fix is to "de-minimize" the PropertyAssignment grammar:
>
> PropertyAssignment:
> PropertyName : AssignmentExpression
> get PropertyName ( ) { FunctionBody }
> set PropertyName ( PropertySetParameterList ) { FunctionBody }
>
> PropertyName:
> IdentifierName
> StringLiteral
> NumericLiteral
>
> to look like this:
>
> PropertyAssignment:
> IdentifierName : AssignmentExpression
> StringLiteral : AssignmentExpression
> NumericLiteral : AssignmentExpression
> get PropertyName ( ) { FunctionBody }
> set PropertyName ( PropertySetParameterList ) { FunctionBody }
>
> PropertyName:
> IdentifierName
> StringLiteral
> NumericLiteral
>
> This works because the lookahead after : in this revised PropertyAssignment
> and in WellLabeledStatement is disjoint except for { and that loops back
> through the same paths, with the tie broken by a disjoint lookahead token,
> eventually.
>
> Is this grammar refactoring worth the trouble? Making blocks be expressions
> could be well worth it if we accept block-lambdas. Just for statements as
> expressions, I'm not sure. Comments welcome.
>
> /be
>
>
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