NIM game (5,4,3,2,1)

nim.hs

-- board type definition for game board
type Board = [Int]
initBoard :: Board
initBoard = [5,4,3,2,1]

-- player tpye definition
data Player = P1 | P2 deriving Show
nextP :: Player -> Player 
nextP P1 = P2
nextP P2 = P1

-- check if hte game is over
is_finished ::Board -> Bool
is_finished b = all (==0) b

-- make a move and return chaned game state
move :: Board -> Int -> Int -> Board
move (x:xs) p o   | p == 0 = ((x-o):xs)
                  | otherwise = x:(move xs (p-1) o)

--  print a row with sticks
putRow :: Int -> Int -> IO()
putRow row sticks = do
    putStr ((show row) ++ ") ")
    putStrLn (map (\_ -> '|') [1..sticks])

-- print entire game board
putBoard :: Board -> IO()
putBoard b = printBoard b 1  where
    printBoard (x:xs) row = do
        putRow row x
        printBoard xs (row + 1)    
    printBoard [] _ = do return ()

-- helper function for etting row number
getRowNum :: String -> IO Int
getRowNum prompt = do
    putStrLn prompt
    rows <- getLine
    return (read rows)
    
-- play the current game, using given board
play :: Board -> Player -> IO()
play board player | is_finished(board) = putStrLn ((show player) ++ " won")
                  | otherwise = do
                    putBoard board
                    putStrLn ("Player " ++ (show player) ++ " is playing")
                    row <- getRowNum "Enter row"
                    sticks <- getRowNum "Enter count of sticks to remove"
                    play (move board (row-1) sticks) (nextP player)

startGame = play initBoard P1

main = do
    startGame