[antlr-interest] add a tree visitor?

[Terence Parr]

On Oct 28, 2008, at 8:15 AM, Andy Tripp wrote:
> Yep, that's the Visitor design pattern...seems like a good thing to  
> add.
> The TreeVisitorAction method is usually called "accept()", though.

I decided to allow both pre-and post:

/** How to execute code for node t when a visitor visits node t.   
Execute
  *  pre() before visiting children and execute post() after visiting  
children.
  */
public interface TreeVisitorAction {
     /** Execute an action before visiting children of t.  Return t or
      *  a rewritten t.  Children of returned value will be visited.
      */
     public Object pre(Object t);

     /** Execute an action after visiting children of t.  Return t or
      *  a rewritten t.  It is up to the visitor to decide what to do
      *  with the return value.
      */
     public Object post(Object t);
}

> And the Java 1.5 foreach and generics would make the code cleaner.

I hate that syntax because it looks so nice, but crashes if you have a  
null list. stupidest thing I've ever seen in my life. plus, I can't  
rely on 1.5 yet.

I agree it would be nice if that syntax did something nice. :) don't  
get me started on how bad the generic stuff works when you want  
List<AST> to work with List<MyAST>. blech. renders it useless. sorry  
to be so negative on a Tuesday morning. Just getting sick of all of  
these Java "enhancements".

Ter