TicTacToe

Diary of a Tic-tac-toe program

module TicTacToe
where

data Board = String

place :: String -> Int -> Char -> String
place [] _ _ = []
place (x:xs) 1 c = c : xs
place (x:xs) n c = x : (place xs (n-1) c)

firstFree :: String -> Int
firstFree (x:xs) | x == ' ' = 1
                 | otherwise = 1 + (firstFree xs)
main = do
  putStrLn "Enter your move:"
  move1 <- getLine
  let move1Num = read move1
  let board1 = place "         " move1Num 'X'
  let board2 = place board1 (firstFree board1) 'O'
  putStrLn ("New board:" ++ board2)

  putStrLn "Enter your move:"
  move2 <- getLine
  let move2Num = read move2
  let board3 = place board2 move2Num 'X'
  let board4 = place board3 (firstFree board3) 'O'
  putStrLn ("New board:" ++ board4)

  putStrLn "Enter your move:"
  move3 <- getLine
  let move3Num = read move3
  let board5 = place board4 move3Num 'X'
  let board6 = place board5 (firstFree board5) 'O'
  putStrLn ("New board:" ++ board6)

  putStrLn "Enter your move:"
  move4 <- getLine
  let move4Num = read move4
  let board7 = place board6 move4Num 'X'
  let board8 = place board7 (firstFree board7) 'O'
  putStrLn ("New board:" ++ board8)

  putStrLn "Enter your move:"
  move5 <- getLine
  let move5Num = read move5
  let board9 = place board8 move5Num 'X'

  putStrLn ("Final board:" ++ board9)

Hideous, isn't it? Why, thank you! That is, in fact, the point. I want to start with an absolutely hideous piece of code, and add features, re-factoring as I go. It seems to me like there's actually a lot you can do with tic-tac-toe, and so I hope this will turn into something instructive, both for me and for anyone who wants to follow along, and/or contribute.

Feature ideas (in no particular order):

• output a real board
• game-end condition check
• curses-based interface
• tic-tac-toe variants
• computer can be x or o
• two-player mode
• tournament mode
• web interface
• lazy alpha-beta player
• random square player
• brute-force player
• computer vs. computer mode
• genetically-evolved players