game.hs

import Data.Char
import Data.List

sumCows :: (Eq a, Num b) => [a] -> [a] -> b
sumCows [] _ = 0
sumCows _ [] = 0
sumCows (x:xs) (y:ys) = current + sumCows (xs++[x]) ys 
  where 
    current = (if (x /= y) && (elem y xs) then 1 else 0)

containsDups lst = lenOrg /= lenDer
  where 
    xs = map toUpper lst
    lenOrg = length xs
    lenDer = length . nub $ xs

playTheGame :: String -> Int -> IO ()
playTheGame isogramWord attemptsNum
  | attemptsNum <= 0 = putStrLn "Jeez, you should allow for at least one attempt to guess.."
  | containsDups isogramWord = putStrLn "You play Bulls'n'Cows only with an isogram words!"
  | otherwise = guessTurn isogramWord attemptsNum

guessTurn :: String -> Int -> IO ()
guessTurn _ attemptsNum
  | attemptsNum <= 0 = putStrLn "Too bad, no more attempts left. You lost!"
guessTurn isogramWord attemptsNum = 
  do 
    putStrLn ("You have "++ (show attemptsNum) ++" attemps left. Make your guess: " ++ ['#' | _ <- isogramWord])
    inputGuess <- getLine
    let
      isogramWord'  = capitalize isogramWord
      inputGuess'   = capitalize inputGuess
      bulls = length . filter (== True) . zipWith (==) isogramWord' $ inputGuess'
      cows  = sumCows isogramWord' inputGuess'
    in
      do 
        putStrLn ("You've got " ++ (show bulls) ++ " bulls and " ++ (show cows) ++ " cows.")
        if bulls == (length isogramWord)     
          then putStrLn "Attaboy! You've just won!"
          else guessTurn isogramWord (attemptsNum-1)

main = do
  putStrLn "Enter your guess"
  word <- getLine
  playTheGame word 5