[antlr-interest] How do I skip a subtree walking in a tree grammar?

[Shihwei Li]

Ok. time to learn more about predicates..

Still got problems. After removing '=>', compilation errors were reduced
from 35 to 34. All erros are the same: 'a' can not be resolved.
         if ( ((a)) ) {s = 18;}
         else if ( (true) ) {s = 19;}

Any idea why? Antlr I am using is 3.1.1

Here is the grammar I touched:

bool_exp returns [boolean value]
    throws ConditionExpressionException
    :
        not_bool_exp                  { $value = $not_bool_exp.value; }
    |
^(OR a=bool_exp
   ( {$a.value}? ignore { $value = true; }
   | b=bool_exp { $value = $b.value; }
   ))
 | ^(AND a=bool_exp
   ( {$a.value}? b=bool_exp { $value = $b.value; }
   | ignore { $value = false; }
   ))
    ;

--peter

2009/3/16 Gavin Lambert <antlr at mirality.co.nz>

> At 09:09 17/03/2009, Shihwei Li wrote:
>
>> Is this related to syntactic predicate? I can sort of understand the idea
>> behind, but I am not familiar with the syntactic predicate yet. So still
>> need some help from you.
>>
>
> These are actually semantic predicates.
>
>  I tried the tree grammar you provided, and I got compilation errors in the
>> generated java code, such as
>>
>>  if ( ((a)) ) {s = 18;}
>>  else if ( (true) ) {s = 19;}
>>
>> Saying that 'a' is not defined.
>>
>
> Ah, ok; looks like the predicates are being hoisted out of context.  Try
> removing the => arrows.  I can never remember when one should be used vs.
> the other :)
>
>
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