[antlr-interest] Problems with semantic predicates

[Johannes Luber]

Haralambi Haralambiev schrieb:
> Hello Johannes,
> 
> So, if I understand correctly, you suggest to have the following (using 
> a scope):
> 
> r2
> : {$r::flag}? Token1 -> ^(NODE Token1)
> | Token1
> ;
> 
> If the above is a correct assumption, then how can I set the scope 
> variable, as I could only think of the following way:
> 
> r
> scope {
>   boolean flag;
> }
> : Token1^ Token2!
>     {$r::flag = true;} 
>     r2
> | Token1^
>   {$r::flag = false;}
>   r2
> ;
> 
> This solution, however, will fail, as the action for setting the scope 
> variable will not be executed until the backtracking is over. But I need 
> this variable set, as it will be used as a predicate for the parsing. 
> Thus, we have a catch-22 situation.
> 
> A solution I could think of is not to have two alternatives for r2, but 
> rather construct the CommonTree manually with java code and within to 
> use the knowledge of the boolean flag. But I dislike this solution and 
> am open to suggestions.

Try using {{$r::flag = true;}}.

Johannes