Re: When %dprec and %merge aren't enough...

[Marcel Laverdet]

This is a pretty good idea, but I'm not sure if it's possible. For  
instance in the case of an if statement I modified my grammar as such:

if_statement:
    t_IF t_LPAREN expression t_RPAREN {yyexpect_statement;} statement  
t_ELSE statement
<...>
|   t_IF t_LPAREN expression t_RPAREN {yyexpect_statement;} statement  
%prec p_IF
<...>
;

Where yyexpect_statement is a macro I defined to set a global flag and  
then the lexer checks and returns an appropriate t_LCURLY for  
statements. The problem I'm seeing here is that the glr parser defers  
my mid-action rule so the lexer can't adjust in time.


On Nov 11, 2008, at 11:08 AM, Hans Aberg wrote:
> On 11 Nov 2008, at 08:10, Marcel Laverdet wrote:
>
> > It's unclear here whether the child of the if statement should be  
> > an empty Block or an empty ObjectLiteral. The ECMAScript spec  
> > addresses this simply:
> > "Note that an ExpressionStatement cannot start with an opening  
> > curly brace because that might make it ambiguous with a Block."
>
> You might try defining two pairs of braces, one for the blocks, an  
> one for the statements. This should disambiguate the grammar. Then  
> set a context switch that tells the lexer which type to return; the  
> switch is changed from the parser.
>
>  Hans