[antlr-interest] If statement for Tree-based Interpreter: is it the correct way to do it?

[Pavel Ganelin]

Hi,

I found that in ANTLR v3 it is more difficult to skip the child for tree 
walker compare with v2. Is it true or it is just learning curve?

Below I attached how I process if statement for a tree-based 
interpreter. Please note that I had to add artificial token EOL while 
building the tree in the parser so that I could position the cursor just 
before Token.UP. I did not find a way to move the pointer to the last 
node of the the given tree ($s in the example below). Start and Stop 
indexes in the tree node point to the original token tree, not the 
CommonTreeNodeStream.

Is it the way it is supposed to be implemented? If not what is the 
correct approach

PS. I did read  
http://www.antlr.org/wiki/display/ANTLR3/Simple+tree-based+interpeter. 
It does not cover this question.

Thanks,
Pavel
==================================================== grammar 
==========================
ifStatement
:
   ^(s=IF  e=eval
        /*
          ^(then=SLIST)
          ^(els=SLIST )
          EOL // artificial token added by parser to help position
              // stream after evaluation

        */
   {
        CommonTreeNodeStream stream = (CommonTreeNodeStream) input;
        Tree then=$s.getChild(1);
        Tree els =$s.getChild(2);

        if ($e.value) {
            input.seek(stream.getNodeIndex(then));
            slist(queue);
        }
        else {
            input.seek(stream.getNodeIndex(els));
            slist(queue);
        }
        input.seek(stream.getNodeIndex($s.getChild(3)));
   }
   EOL)
;

//   evaluates the expression

eval returns [bool value] :
^(EXPR
    ....

);

//   process statements:
  ^(SLIST
....

)
;