Hi Doug:

Johan and I had an interesting discussion about traversing
into terminal classes, such as Ident, String.

So far I have thought that we never want to traverse into those classes
since they are predefined (many of them by Java) and we cannot modify
them.

Johan was pointing out that this view of the world is not correct when 
we have generic visitors. 

For 

A = Ident.

the generic printing visitor is:

PrintVisitor {
  before -> A, ident, Ident (@
      space();
	  out.print(source.get_ident());
	      needSpace = true;
		@)
which means we have to traverse into Ident so that we go through the
edge A, ident, Ident.

Therefore, the correct view is:

It is ok to traverse to terminal classes provided no code is defined for
them. When you use generic visitors, you are required to traverse
to the terminal classes if you want to process them by the generic visitors.

Do you agree?

-- Karl