prolog in scheme

[Tim Finin <Tim@cis.upenn.edu>]

We tried using the query system in "Structure & Interpretation" in our
freshman class last year and found it wanting in some respects.  (1) It
doesn't handle disjunctions unless the disjuncts contain the same variables.
(2) It is extremely slow. We were using it in TI's PC Scheme on AT's.  We
gave some very simple logic programming problems (e.g. the standard kinship
relations) and found that the students we spending 10 or 15 minutes waiting
for the query system to finish!  They found this very frustrating.

I'd think I would like to cover the query system from S&I in class because
it's clear and simple and have the students use a more suped-up version that
is reasonably efficient.  In addition, facilities like "retract",
"reconsult", etc. would easy it's use in homeworks.

I'd also like to consider using a system which uses a prolog-like
depth-first backtracking search.

Tim