🚀 go-pugleaf

F(Type) - The desired function to apply to elements of type.

iterator(Type) - a function that returns the next valid element of
		 Type according to some rule, if one exists; null
		 otherwise

traverser(Type) - a function that, for every iteration T of Type, F(T)
		  is evaluated

I suppose you can see what I'm getting at.  Supplying a function to
the traverser is equivalent to:

    while (T = iterator(Type)) do F(T)

This is easy enough to do in most programming languages.  Even pascal
allows you to pass subprograms to other subprograms.

I can't count the number of traversals I've written like this:

/****************************************************************\
* preorder: apply F to every subtree of T, ordered by a preorder *
*	    traversal						 *
\****************************************************************/
preorder(tree T, function F(tree))
  if T, F(T)
	preorder(left(T), F)
	preorder(right(T), F)
			     ___
		    Cheers,  \o/  Silver
      201-932-2443 (mostly)   V   (internet) gaynor@rutgers.edu
      201-545-0458 (rarely)  _|_  (uucp)     ...!rutgers!gaynor