Friends at Hogwarts

hogwarts.pl

% Prolog: How Hogwarts students decide their friends.
% (Very incomplete!)
%
% Try at http://swish.swi-prolog.org/
% ?- friend(X, draco).
% X = harry.
% X = tom.
%

purebloodish(W) :- child(W, P), child(W, Q),
                   magical(P), magical(Q),
                   P \= Q.
halfblood(W) :- child(W, P), child(W, Q),
                magical(P),
                not(magical(Q)),
                P \= Q.
mudblood(W) :- child(W, P), child(W, Q),
               not(magical(P)),
               not(magical(Q)),
               P \= Q.
squib(S) :- child(S, P),
            magical(P),
            not(magical(S)).
friend(F, P) :- not(slytherin(P)), magical(F).
friend(F, _) :- magical(F), purebloodish(F).
friend(F, _) :- magical(F), halfblood(F).

child(harry, james).
child(harry, lily).
child(hermionie, dentist1).
child(hermionie, dentist2).
child(tom, tomsr).
child(tom, merope).
child(argus, argusdad).
child(argus, argusmum).
magical(james).
magical(lily).
magical(merope).
magical(harry).
magical(hermionie).
magical(tom).
magical(argusmum).
magical(draco).
slytherin(draco).