[antlr-interest] Problems with semantic predicates

[Haralambi Haralambiev]

Hello,

First of all, thanks for the magnificent tool. I
consider myself new to advanced stuff, as I have been working with it
for less than a month.

So, the problem that I currently cannot resolve is described by the
following test grammar:

----------
grammar test;

options {
output=AST;
ASTLabelType=CommonTree;
backtrack=true;
memoize=true;
}

tokens
{
NODE;
}

r : Token1^ Token2! r2[true]
| Token1^ r2[false]
;
r2[boolean flag]
: {flag}? Token1 -> ^(NODE Token1)
| Token1
;

Token1 : 'TOKEN1';
Token2 : 'TOKEN2';
----------

The general idea is that depending on how one rule matches, I would like a
subrule to generate the AST differently.

I decided to do this with some boolean flag, but
the problem is that the generated Java parser class cannot compile.
In the example above - the method *synpred2_fragment()* contains a statement
*if ( !(flag) )* but the variable flag cannot be resolved.

So, if you could please guide me how to resolve this problem. Maybe I have
missed something fundamental in my understandings for developing the
grammar.

Thank you in advance!

Best Regards,
Hari
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