[antlr-interest] add a tree visitor?

[Terence Parr]

Howdy, as part of my tree grammar filter mode, I need an external tree  
visitor. It's just a depth first walk that triggers a pattern match  
for each node as it walks back up the tree. I might as well make it a  
generic action, which means I need an interface in Java. [java doesn't  
have function pointers...sigh]

     public interface TreeVisitorAction {
         public void visit(Object t);
     }

Then the depth first recursive walk can trigger a generic action after  
visiting the children, us, doing a bottom-up walk:

    public static void visit(CommonTree t, TreeVisitorAction action) {
         if ( t.getChildCount()>0 ) {
             List children = t.getChildren();
             for (int i=0; i<children.size(); i++) {
                 CommonTree child = (CommonTree)children.get(i);
                 filter(child, action);
             }
         }
         action.visit(t);
     }

Is this a reasonable bit of code to insert in the main distribution?   
C and other languages can use function pointers to perform the true  
intent of the interface.

Such a plain "visit every node" visitor is not particularly useful  
unless the triggered action does something interesting. In my case, I  
tell it to try to match one of the tree patterns:

        public static void filter(CommonTree t) {
             filter(t, new TreeVisitorAction() {
                 public void visit(Object t) { match((CommonTree)t); }
             });
         }

where match(t) creates a tree parser and tries to match that subtree  
to one of the patterns.

Ter