[antlr-interest] Rule-local variables?

[Vaclav Barta]

Hi,

skimming http://www.antlr.org/works/help/tutorial/calculator.html, I've 
noticed ANTLR rules can be declared to return a value, which can be set 
in the rule's actions, often from results produced by lower-level rules 
- say

whereClause returns [ IExpression value ] :
	WHERE c = searchCondition { $value = $c.value; }
	;

That works, but I'd also like to have conditions depending on how ANTLR 
got to a rule and its action. Negation is a typical example:

predicate returns [ IExpression value ] :
	( NOT { (A) } )?
		( LIKE ... { (B) }
		| e = expression { (C) }
		)
	;

How do I know in (B) and (C) that I've passed through (A) (and therefore 
have to generate a NOT LIKE operator and a negated expression)? I can do

predicate returns [ IExpression value ] :
	NOT {
		$value = new Expression();
		((Expression)$value).Operator = ExpressionOperator.Not;
	} ( LIKE ... { if ($value == null) ... else ... }
		| e = expression { if ($value == null) ... else ... }
		)
	;

but in more complicated cases, when nested branches store their internal 
state into the same variable, it gets confusing and ugly pretty fast - 
so I'd like to have a local flag meaning "this expression has been 
negated" and nothing else. How can I do that in ANTLR?

	Bye
		Vasek