Haskellmind: A Haskell CLI implementation of Mastermind

haskellmind.hs

import System.Random
import Data.Char (isDigit)

makeCode :: IO [Char]
makeCode = do
  gen <- newStdGen
  return $ take 4 (randomRs ('0','9') gen)

breakCode :: String -> Int -> IO ()
breakCode code turns = do
  putStrLn $ " Turns left: " ++ show turns
  answer <- getLine
  if length answer /= 4 || not (all isDigit answer)
     then requireValidInput code answer turns
     else provideFeedback code answer turns

provideFeedback :: String -> String -> Int -> IO ()
provideFeedback code guess turns = do
  let rest = filter (\(x,y) -> x /= y) (zip guess code)
  let correct = (length code) - (length rest)
  let present = length (filter (\(x,y) -> x `elem` code) rest)
  putStr " Feedback: "
  putStr (take correct (repeat '●'))
  putStr (take present (repeat '○'))
  putStrLn (take ((length code) - correct - present) (repeat '-'))
  turn code guess (turns - 1)

requireValidInput :: String -> String -> Int -> IO ()
requireValidInput code guess turns = do
  putStrLn " Oops, answer must be four numbers"
  turn code guess turns

turn :: String -> String -> Int -> IO ()
turn code guess turns = do
  if turns == 0
     then putStrLn "You lose"
     else if code == guess
             then putStrLn "You win!"
             else breakCode code turns

haskellmind :: IO ()
haskellmind = do
  let turns = 12
  code <- makeCode
  turn code ['-' | x <- code] turns