% A Tic-Tac-Toe program in Prolog. S. Tanimoto, May 11, 2003.
% To play a game with the computer, type
% playo.
% To watch the computer play a game with itself, type
% selfgame.
% Predicates that define the winning conditions:
win(Board, Player) :- rowwin(Board, Player).
win(Board, Player) :- colwin(Board, Player).
win(Board, Player) :- diagwin(Board, Player).
rowwin(Board, Player) :- Board = [Player,Player,Player,_,_,_,_,_,_].
rowwin(Board, Player) :- Board = [_,_,_,Player,Player,Player,_,_,_].
rowwin(Board, Player) :- Board = [_,_,_,_,_,_,Player,Player,Player].
colwin(Board, Player) :- Board = [Player,_,_,Player,_,_,Player,_,_].
colwin(Board, Player) :- Board = [_,Player,_,_,Player,_,_,Player,_].
colwin(Board, Player) :- Board = [_,_,Player,_,_,Player,_,_,Player].
diagwin(Board, Player) :- Board = [Player,_,_,_,Player,_,_,_,Player].
diagwin(Board, Player) :- Board = [_,_,Player,_,Player,_,Player,_,_].
% Helping predicate for alternating play in a "self" game:
other(x,o).
other(o,x).
game(Board, Player) :- win(Board, Player), !, write([player, Player, wins]).
game(Board, Player) :-
other(Player,Otherplayer),
move(Board,Player,Newboard),
!,
display(Newboard),
game(Newboard,Otherplayer).
move([b,B,C,D,E,F,G,H,I], Player, [Player,B,C,D,E,F,G,H,I]).
move([A,b,C,D,E,F,G,H,I], Player, [A,Player,C,D,E,F,G,H,I]).
move([A,B,b,D,E,F,G,H,I], Player, [A,B,Player,D,E,F,G,H,I]).
move([A,B,C,b,E,F,G,H,I], Player, [A,B,C,Player,E,F,G,H,I]).
move([A,B,C,D,b,F,G,H,I], Player, [A,B,C,D,Player,F,G,H,I]).
move([A,B,C,D,E,b,G,H,I], Player, [A,B,C,D,E,Player,G,H,I]).
move([A,B,C,D,E,F,b,H,I], Player, [A,B,C,D,E,F,Player,H,I]).
move([A,B,C,D,E,F,G,b,I], Player, [A,B,C,D,E,F,G,Player,I]).
move([A,B,C,D,E,F,G,H,b], Player, [A,B,C,D,E,F,G,H,Player]).
display([A,B,C,D,E,F,G,H,I]) :- write([A,B,C]),nl,write([D,E,F]),nl,
write([G,H,I]),nl,nl.
selfgame :- game([b,b,b,b,b,b,b,b,b],x).
% Predicates to support playing a game with the user:
x_can_win_in_one(Board) :- move(Board, x, Newboard), win(Newboard, x).
% The predicate orespond generates the computer's (playing o) reponse
% from the current Board.
orespond(Board,Newboard) :-
move(Board, o, Newboard),
win(Newboard, o),
!.
orespond(Board,Newboard) :-
move(Board, o, Newboard),
not(x_can_win_in_one(Newboard)).
orespond(Board,Newboard) :-
move(Board, o, Newboard).
orespond(Board,Newboard) :-
not(member(b,Board)),
!,
write('Cats game!'), nl,
Newboard = Board.
% The following translates from an integer description
% of x's move to a board transformation.
xmove([b,B,C,D,E,F,G,H,I], 1, [x,B,C,D,E,F,G,H,I]).
xmove([A,b,C,D,E,F,G,H,I], 2, [A,x,C,D,E,F,G,H,I]).
xmove([A,B,b,D,E,F,G,H,I], 3, [A,B,x,D,E,F,G,H,I]).
xmove([A,B,C,b,E,F,G,H,I], 4, [A,B,C,x,E,F,G,H,I]).
xmove([A,B,C,D,b,F,G,H,I], 5, [A,B,C,D,x,F,G,H,I]).
xmove([A,B,C,D,E,b,G,H,I], 6, [A,B,C,D,E,x,G,H,I]).
xmove([A,B,C,D,E,F,b,H,I], 7, [A,B,C,D,E,F,x,H,I]).
xmove([A,B,C,D,E,F,G,b,I], 8, [A,B,C,D,E,F,G,x,I]).
xmove([A,B,C,D,E,F,G,H,b], 9, [A,B,C,D,E,F,G,H,x]).
xmove(Board, N, Board) :- write('Illegal move.'), nl.
% The 0-place predicate playo starts a game with the user.
playo :- explain, playfrom([b,b,b,b,b,b,b,b,b]).
explain :-
write('You play X by entering integer positions followed by a period.'),
nl,
display([1,2,3,4,5,6,7,8,9]).
playfrom(Board) :- win(Board, x), write('You win!').
playfrom(Board) :- win(Board, o), write('I win!').
playfrom(Board) :- read(N),
xmove(Board, N, Newboard),
display(Newboard),
orespond(Newboard, Newnewboard),
display(Newnewboard),
playfrom(Newnewboard).
