import Prelude
 
-- Excercise of Lecture 9 of "Programming Haskell"
 
data Player = PlayerOne | PlayerTwo deriving Show
nextPlayer PlayerOne = PlayerTwo
nextPlayer _         = PlayerOne
 
nim :: Player -> [Int] -> IO ()
nim player xs   | sum xs == 0 = putStrLn $ show (nextPlayer player) ++ " has won!"
   | otherwise = 
         let rmStar :: [Int] -> Int -> Maybe [Int]
             rmStar xs n 
                  | xs !! n == 0 = Nothing
                  | otherwise = Just (rmStar' xs n)
                  where
                     rmStar' xs 0 = xs !! 0 - 1 : drop 1 xs
                     rmStar' (x:xs) (pos+1) = x : rmStar' xs pos
              dsplStandings :: [Int] -> IO ()
             dsplStandings = dsplStandings' 0 
                  where
                     dsplStandings' 5 _ = return ()
                     dsplStandings' n xs = do
                           putStr $ show (n+1) ++ ": "
                           putStrLn $ take (xs !! n) (repeat '*')
                           dsplStandings' (n+1) xs 
 
         in do            dsplStandings xs
            putStr $ show player ++ ", "
            putStr "From which row do you want to remove a star?: "
            x <- getChar
            let pos = read (x:[]) - 1 
            if or [(pos < 0),(pos >= 5)] then do
                  putChar '\n'
                  putStrLn "This row is out of range!"
                  nim player xs
             else do                  putChar '\n'
                  case rmStar xs pos of
                     Just decr -> nim (nextPlayer player) decr
                     Nothing -> do
                        putStr "This row is already empty!"
                        putStrLn " Take another one!"
                        nim player xs
      
 
nimTest = nim PlayerOne [1..5]{- Bsp.:
*Main> nimTest
1: *
2: **
3: ***
4: ****
5: *****
PlayerOne, From which row do you want to remove a star?: 1
1: 
2: **3: ***
4: ****
5: *****
PlayerTwo, From which row do you want to remove a star?: 6
This row is out of range!
1: 
2: **
3: ***
4: ****
5: *****PlayerTwo, From which row do you want to remove a star?: 4
1: 
2: **
3: ***
4: ***
5: *****
PlayerOne, From which row do you want to remove a star?: 3
1: 
2: **
3: **4: ***
5: *****
PlayerTwo, From which row do you want to remove a star?: 2
1: 
2: *
3: **
4: ***
5: *****
PlayerOne, From which row do you want to remove a star?: 3
1: 2: *
3: *
4: ***
5: *****
PlayerTwo, From which row do you want to remove a star?: 5
1: 
2: *
3: *
4: ***
5: ****PlayerOne, From which row do you want to remove a star?: 6
This row is out of range!
1: 
2: *
3: *
4: ***
5: ****
PlayerOne, From which row do you want to remove a star?: 7
This row is out of range!
1: 2: *
3: *
4: ***
5: ****
PlayerOne, From which row do you want to remove a star?: 5
1: 
2: *
3: *
4: ***
5: ***PlayerTwo, From which row do you want to remove a star?: 5
1: 
2: *
3: *
4: ***
5: **
PlayerOne, From which row do you want to remove a star?: 5
1: 
2: *
3: *4: ***
5: *
PlayerTwo, From which row do you want to remove a star?: 5
1: 
2: *
3: *
4: ***
5: 
PlayerOne, From which row do you want to remove a star?: 4
1: 2: *
3: *
4: **
5: 
PlayerTwo, From which row do you want to remove a star?: 3
1: 
2: *
3: 
4: **
5: PlayerOne, From which row do you want to remove a star?: 2
1: 
2: 
3: 
4: **
5: 
PlayerTwo, From which row do you want to remove a star?: 4
1: 
2: 
3: 4: *
5: 
PlayerOne, From which row do you want to remove a star?: 4
PlayerOne has won!
*Main> 
-}