% Generic puzzle solver
%   ---- Try possibillities against given facts and assert those that fit
%        Each component can only occur once in a fact
solution(X):-
	possibility(X),
	unknown(X),
	givens(X),
	assertz(fact(X)).

% --- the following avoids a warning ----
:-style_check(-singleton).
% --- the following avoids an exception ----
:-dynamic(fact/1).

% normally X will be a structure with components representing different
% facets of the entities involved.

%  --- two utilities: if-then-, and if-and-only-if
if(P,Q):- P->Q;true.
iff(P,Q):-(P,Q); not( P ), not( Q ).

% Test case
% A Sample Logic Problem. [ Original logic problems, July 1990, p 5]
% Angela, David and Mae are the young stars in a talent show.
% Their ages are 5,7, and 8. One has last name Starr.
% Miss Grant is three years older than Angela.
% The child whose last name is Diamond is seven years old
%
first(angela). first(david). first(mae).
male(david). female(angela). female(mae).
age(5). age(7). age(8).
last(diamond). last(grant). last(starr).

possibility(child(First,Last,Age)):-first(First), last(Last), age(Age).

givens(child(First,Last,Age)):-
	if(male(First), Last\=grant),
	if(Last=grant, female(First)),
	iff(Last=diamond,Age=7),
	iff(Last=grant,Age=8),
	iff(First=angela,Age=5).

unknown(child(First,Last,Age)):- not( fact(child(First,_,_))),
	not( fact(child(_,Last,_))),
	not( fact(child(_,_,Age))).


go:-solution(X), fail; listing(fact).

:- write('Puzzle loaded'), nl,nl.
:- write('Input time(go). to start solving it... and see how fast it is.'), nl,nl.