#!/usr/bin/perl
use strict;
use warnings;
use AI::Prolog;

my $prolog = AI::Prolog->new(<<END_PROLOG);
parent(sally, tom).
parent(bill, tom).
parent(tom, sue).
parent(alice, sue).
parent(sarah, tim).

male(bill).
male(tom).
male(tim).

father(Person) :-
    parent(Person, _),
    male(Person).
END_PROLOG

$prolog->query('father(Whom)');
while (my $results = $prolog->results) {
    print "@$results\n";
}
__END__
father bill
father tom