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% 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).
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