Well, I couldn't sleep last night. I kept tossing and turning while thinking about how to get math working right. I got up early and rather than implement the complete parser solution, I went ahead and used predicates instead of operators for math. It's clumsy, but it is how Prolog works underneath the hood:
% X is 3 + 4. is(X, plus(3,4)). % Once again: patches welcome :)
The snippet above binds X to 7 (obviously). The predicates I have working are:
plus(X,Y). minus(X,Y). mult(X,Y). div(X,Y). mod(X,Y). is(X,Y). ge(X,Y). gt(X,Y). le(X,Y). lt(X,Y).
Unfortunately, I can only declare integer numbers (though the math supports floats), but that's a limitation of my parser. I'll fix that.
What this means, however, is after some polishing, the Prolog engine is mostly feature complete. Yeah, I can use a new parser, but I'm not too worried about that right now. Instead, since I have the features I want, I can get this ready for distribution and start working on performance. For example, I've written a tiny scheduling program. It's very slow. However, the Towers of Hanoi is very fast :)
#!/usr/bin/perl
use strict;
use warnings;
use AI::Prolog;
my $prolog = AI::Prolog->new(<<'END_PROLOG');
hanoi(N) :-
move(N, left, center, right).
move(0, NULL1, NULL2, NULL3) :- !.
move(N,A,B,C) :-
is(M, minus(N,1)),
move(M,A,C,B),
inform(A,B),
move(M,C,B,A).
inform(X,Y) :-
print("Move a disc from the "),
print(X),
print(" pole to the "),
print(Y),
println(" pole").
END_PROLOG
$prolog->do('hanoi(4)');
Hopefully I'll have something uploaded by this weekend.