[antlr-interest] ANTLR 2.7.7 TreeParser transformation question

[Kevin J. Cummings]

language = C++

I'm trying to do a tree transformation before I generate some code from 
the resulting tree.  So, I have the following set of rules in my tree 
walker:

> bexpr : #( AND a1:bexpr a2:bexpr )
>       | #( OR  o1:bexpr o2:bexpr )
>       | #( NOT n:bexpr )
>       | #( LESSTHAN lt1:aexpr lt2:aexpr )
>       | #( LE       le1:aexpr le2:aexpr )
>       | #( GT       gt1:aexpr gt2:aexpr )
>       | #( GE       ge1:aexpr ge2:aexpr )
>       | #( EQ       eq1:aexpr eq2:aexpr )
>       | #( NE       ne1:aexpr ne2:aexpr )
>       ;
> 
> // Lets fold constant expressions out below
> // and emit the final code for aexpr when they get used above.
> aexpr :! #( PLUS  p1:aexpr p2:aexpr )
>          { 
>          // Anything plus 0 is Anything
>            if (isZero(p1))
>               { 
>                 #aexpr = #p2;
>               }
>            else if (isZero(p2))
>               { 
>                 #aexpr = #p1;
>               }
>            else
>               { 
>                 #aexpr = #(PLUS, p1, p2);
>               }
>          }
>       |! ( #( MINUS aexpr aexpr ) )=> #( minus:MINUS m1:aexpr m2:aexpr )
>       |! #( mult:MULT mu1:aexpr mu2:aexpr )
>       |! #( div:DIV d1:aexpr d2:aexpr )
>       |! #( neg:MINUS n:aexpr )
>       | NUM
>       | STRING
>       ;

What I'm trying to do is transform the tree passed into aexpr in those 
cases when I can remove complexity.  My isZero() method is correctly 
recognizing those NUM trees which contain the number "0".
If I examine #aexpr before leaving this rule, I can see that:
	(PLUS 2 0)
is correctly reduced to just
         2

My problem is that the assignment to #aexpr appears in the .cpp code as
a reference to:   aexpr_AST_in, but it is never used again after it gets 
assigned!

The end of the case continues with assigning _retTree = _t and not my 
new tree.  The result of this is that when I examine my aexpr subtree in 
the bexpr rule, it is the original (PLUS 2 0) tree!  Not the transformed 
one!

So what's the point of assigning it if it never gets returned?

Am I doing something wrong?

-- 
Kevin J. Cummings
kjchome at rcn.com
cummings at kjchome.homeip.net
cummings at kjc386.framingham.ma.us
Registered Linux User #1232 (http://counter.li.org)