Java Tree Builder by Jens Palsberg and Kevin Tao:

http://www.cs.purdue.edu/homes/taokr/jtb/tools.html

1. A very well done home page which explains the tool.
   It is refreshing to see that the visitor pattern gets wider use.
   SUN's JJTree also uses visitors aparently based on input from Jens.

   One summary of the Visitor Design Pattern is:

   The Visitor pattern lets us define a new operation on 
   an object structure without changing the classes of the
   objects on which it operates.

   Bu that is also the summary for a propagation pattern which we used
   already in the early 90's. 
   
   A propagation pattern lets us define a new operation on 
   an object structure without changing the classes of the
   objects on which it operates.

   The visitor pattern proposes an implementation
   in terms of visitor objects. 
   Propagation patterns were implemented differently by inlining
   the visitor object code.
   But the interface is the same. Our first propagation pattern publication 
   was in July 1992 and then in September 1992.

2. We could use Jen's approach and use the JavaCC grammar notation to define
   class dictionaries. If JavaCC becomes popular, we should add such
   a standard interface.

3. Demeter/Java goes beyond JTB and JJTree:
   - we generate a larger visitor library, like a CopyVisitor, DisplayVisitor,
     EqualVisitor, PrintVisitor etc.
   - we define traversals succinctly, using strategies.
   - our visitors are more refined: before/after/around methods on edges
     and nodes, return and init methods, etc.

-- Karl