chapter10_nim.hs

import Data.Char

next :: Int -> Int
next 1 = 2
next 2 = 1

type Board = [Int]
 
initial :: Board
initial = [5, 4, 3, 2, 1]

finished :: Board -> Bool
finished = all (== 0)

valid :: Board -> Int -> Int -> Bool
valid board row num = board !! (row - 1) >= num

move :: Board -> Int -> Int -> Board
move board row num = [update r n | (r, n) <- zip [1..] board]
    where update r n = if r == row then n - num else n

putRow :: Int -> Int -> IO ()
putRow row num = do putStr (show row)
                    putStr ": "
                    putStrLn (concat (replicate num "* "))

putBoard :: Board -> IO ()
--putBoard [a, b, c, d, e] = do putRow 1 a
--                              putRow 2 b
--                              putRow 3 c
--                              putRow 4 d
--                              putRow 5 e

--hw10 2
--putBoard b = putBoardAux (zip [1..] b)
--putBoardAux [] = return ()
--putBoardAux ((r, n):xs) = do putRow r n
--                             putBoardAux xs
--

--hw10 3
putBoard b = sequence_ [putRow r n | (r, n) <- zip [1..] b]

getDigit :: String -> IO Int
getDigit prompt = do putStr prompt
                     x <- getChar
                     newline
                     if isDigit x then
                        return (digitToInt x)
                     else
                        do  putStrLn "ERROR: Invalid digit"
                            getDigit prompt 


newline :: IO ()
newline = putChar '\n'

play :: Board -> Int -> IO ()
play board player = 
    do newline
       putBoard board
       if finished board then
            do newline
               putStr "Player "
               putStr (show (next player))
               putStrLn " wins!!"
       else
            do newline
               putStr "Player "
               putStrLn (show player)
               row <- getDigit "Enter a row number: "
               num <- getDigit "Stars to remove: "
               if valid board row num then
                    play (move board row num) (next player)
               else
                    do newline
                       putStrLn "ERROR: Invalid move"
                       play board player

nim :: IO ()
nim = play initial 1