[antlr-interest] How to implement an IF

[ugol]

Hi, I am a complete newbie of ANTLR. I am using the 3.0b5 release and
I am trying to adapt the example found here:

http://www.antlr.org/wiki/display/ANTLR3/Expression+evaluator

I want to add to the expression evaluation a conditional expression:

f.e.

if (x>10) x=y

I think I have correctly built the lexer and parser stuff, but I can't
figure out how to check the condition and then act. My tree stuff
parse the condition, no matter if the condition is true or false. I am
probably missing something here.

I have a IF node with a condition and an expression, but don't know
how to say this:

if ($cond.value() assign.??? )

I was thinking to set some sort of variable and then check it, but I
don't know if this is the right way to do it, and the v3examples
didn't help.

TIA,
uL

Attached two fragments of Cond.g and Eval.g

grammar Cond;
options {
    output=AST;
    ASTLabelType=CommonTree; // type of $stat.tree ref etc...
}

prog
    :   ( stat {System.out.println($stat.tree.toStringTree());} )+ ;

stat
    :   IF LPAREN condition RPAREN assign NEWLINE -> ^(IF condition assign)
    |   assign NEWLINE  -> assign
    |   expr NEWLINE    -> expr
    |   NEWLINE         ->
    ;

assign
    : VAR ASSIGN expr -> ^(ASSIGN VAR expr)
    ;

[cut]

tree grammar Eval;

options {
    tokenVocab=Cond;
    ASTLabelType=CommonTree;
}

@header {
import java.util.HashMap;
}

@members {
}

prog:   stat+ ;

stat:   expr
        {System.out.println($expr.value);}
    |   ^(ASSIGN VAR expr)
        {Memory.put($VAR.text, new Integer($expr.value));}
    |   ^(IF condition assign)
        {if ($condition.value) // how to reference the assign part here?}    ;

condition returns [boolean value]
    :  ^(EQUALS a=expr b=expr) {$value = (a == b);}
    ;