INTERFACEThis interface defines the type representing the players, and the board position of the gameGameBoard ; IMPORT GameMove, MoveList;
BoardSize is the size of the board
CONST BoardSize = 3;
TYPE
(* There are two players, PlayerA and PlayerB. Neither represents
neither player, and is defined for convenience. We will consider that
every cell on the board has a value which is a Player -- the value
PlayerId.PlayerA will indicate that one of player A's pieces on the
square, while PlayerId.Neither will indicate that neither player
occupies that square. *)
PlayerId = {PlayerA, PlayerB, Neither};
Square = GameMove.Square;
Move = GameMove.T;
(* T is the type of a board *)
T <: Public;
Public = OBJECT
METHODS
Init (): T;
squareContents (square: Square): PlayerId;
moveNumber (): CARDINAL;
toMove (): PlayerId;
legalMoves (): MoveList.T;
finished (VAR (*OUT*) winner: PlayerId): BOOLEAN;
previous (): T;
Move (move: Move): T;
END;
The methods of T are as follows. Methods whose names begin with small
letters give information about the state of the board, while methods
starting with capital letters perform some action. No methods have
side-effects upon the board except for Init.
Init initializes the board.
squareContents returns the player whose piece occupies the given square. PlayerId.Neither indicates the square is empty.
moveNumber indicates how many turns have passed, where the game begins with moveNumber 0
toMove returns the player whose turn it is to move
legalMoves returns the list of legal moves that the moving player can make
finished returns TRUE iff the game is over. If it returns TRUE, then winner is set to the player who won. If winner = PlayerId.Neither, then the game ended in a tie.
previous returns the board position before the last move, or NIL IF this board is the first move of the game
Move takes a move, and returns a new board, reflecting that move
END GameBoard.