scheme in prolog

[tim@linc.cis.upenn.edu (Tim Finin)]

The points that Ken, Mike and Paul make are quite valid and very
interesting.  Implementing an interpreter for a language with side
effects in a language without them is bit of a problem and leads to
some known tradeoffs.  The mutable array example is a case in point.

However, Prolog, as opposed to a purer and more abstact logic
programming language does have side effects.  One is free, if one
chooses, to dynamically assert and retract clauses in the database.  I
was, in general, pleased with the way my scheme-in-prolog interpreter
turned out, except when it came to implementing SET!.  I was surprised
that Prolog's side-effecting operations did not enable handle this in
what I considered a good way.  
Tim