[SOLVED] haskelltictactoe.hs

The board

For flexibility, we define constants for the row and column size of the board, length of a winning sequence, and search depth for the game tree:

 rows :: Int rows = 6

 cols :: Int cols = 7

 win :: Int win = 4

 depth :: Int depth = 6

The board itself is represented as a list of rows, where each row is a list of player values, subject to the above row and column sizes:

 type Board = [Row]

 type Row = [Player]

In turn, a player value is either a nought, a blank, or a cross, with a blank representing a position on the board that is not yet occupied:

 data Player = O | B | X deriving (Ord, Eq, Show)

For example, here is a typical board:

 test :: Board test = [[B,B,B,B,B,B,B],

 [B,B,B,B,B,B,B], [B,B,B,B,B,B,B], [B,B,B,X,X,B,B], [B,B,O,O,X,B,B], [B,O,O,X,X,X,O]]

The user interface

The following code displays a board on the screen:

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 showBoard :: Board -> IO () showBoard b =

putStrLn (unlines (map showRow b ++ [line] ++ [nums]))where

 showRow= map showPlayer line = replicate cols - nums = take cols [0..]

 showPlayer :: Player -> Char showPlayer O = O showPlayer B = . showPlayer X = X

For example, showBoard test gives the following output:

 ....... ....... ....... ...XX.. ..OOX.. .OOXXXO ------- 0123456

Exercise

Write a Haskell program

main :: IO ()

that allows a human player to play connect four against the computer, using game trees and the minimax algorithm (as explained in the lectures) to im- plement the computer player. Your solution should aim to be independent of the precise values of the constants row, cols, win and depth.

Hint: construct your program from the bottom-up, starting by defining a number of utility functions on rows and boards, and only then proceeding to think about game trees, minimax, and the user-interface.

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