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lib/AI/Prolog/Article.pod  view on Meta::CPAN

  Programming is not a skill one develops in five easy lessons.

  -- Tom Christiansen

By now, many Perl programmers know that the language offers support for
imperative, objective, and functional programming.  However, logic programming
seems to be a lost art.  This article attempts to shed a little light on the
subject.  It's not that Prolog can do things that Perl cannot or vice versa.
Instead, Prolog does some things more naturally than Perl -- and vice versa.
In fact, while I introduce you to Prolog, I won't be teaching a bunch of nifty
tricks to make your Perl more powerful.  I can't say what needs you may have
and, in any event, the tools that allow logic programming in Perl are generally
alpha quality, thus making them unsuitable for production environments.

=head2 What is Logic Programming?

Logic programming is somewhat of a mystery to many Perl programmers because,
unlike imperative, objective, and functional styles, Perl does not have direct
support for logic programming.   There is, however, much interest in bringing
logic programming to Perl 6.  With luck the information presented here will not
be merely theoretical.

lib/AI/Prolog/Cookbook.pod  view on Meta::CPAN

 reverse([Head|Tail], Reverse) :- 
    reverse(Tail, ReverseTail), 
    append(ReverseTail, [Head], Reverse).

For this, you take the tail of the list, reverse it and append the head of the
list to it.  However, this runs in C<O(N^2)>.  This runs so slowly that
reversing a 30 element list takes 496 logical inferences.  As a result, the
naive reverse is frequently used as a benchmarking tool for logic programs.

If reversing a 30 element list via the naive reverse takes .1 seconds, we can
say that the Prolog implementation is running at about 5000 logical inferences
per second.  This is known by the unfortunate acronym of LIPS, the standard
measure of the speed of logic programs.  Modern Prolog implementations
frequently measure their performance in MLIPS, or MegaLIPS.  By contrast, the
human mind is frequently estimated to run between 1 to 4 LIPS.  This
demonstrates that there's much more to cognition than logic.

=head2 Checking if a list is a subset of another list.

Usage:  C<subset(Subset, List).>