[antlr-interest] How to interpret an IF with antlr 3.0

[Terence Parr]

On May 5, 2007, at 1:21 PM, ugol wrote:

> Hi all,
> I am back with the same question. 3 months ago I rolled back to
> javacc, which I know marginally better, but now I really want to move
> to antlr. Unfortunately, I can't figure out how to delay the
> processing of a node... (if this is the correct solution)
>
> If you don't want to read all this old thread, the question is:
>
> - How to translate this antlr v2 in antlr v3?
>
> ^(IF condition x:.)        // x is NOT evaluated, merely captured
>   { if ($condition.value) { stat(x); }
>
> tia,

Hi Ugol,

first, thanks for updating the wiki on @finally/finally.

ok, to your question.  ANTLR v3 does allow '.' now to mean scan past  
entire tree w/o parsing.  From there you have to create another node  
stream and invoke the rule.  I'll come up with a short hand soon.   
This is from the tree-based interpreter example:

call returns [int value]
@init {
     Map argScope = new HashMap();
     scopes.push(argScope); // push new arg scope
}
     :   ^(CALL ID expr)
         {
         CommonTreeNodeStream stream = (CommonTreeNodeStream)input;
         CommonTree funcRoot = (CommonTree)functions.get($ID.text);
         int addr = stream.getNodeIndex(funcRoot);
         if ( addr>=0 ) {
            CommonTree argNode = (CommonTree)funcRoot.getChild(1);
            String argName = argNode.getText();
            int exprIndex = addr + 4; // skip over FUNC DOWN ID ID to  
expr
            argScope.put(argName, new Integer($expr.value));
            ((CommonTreeNodeStream)input).push(exprIndex);
            $value = expr(); // invoke expr and set CALL's value
            ((CommonTreeNodeStream)input).pop();
         }
         else {
            System.err.println("no such function: "+$ID.text);
         }
         }
     ;
finally {
     scopes.pop();          // remove arg scope
}

Ter