Challenge 9 (Haskell)

import qualified Data.Char as Char
import qualified Data.Map as Map

main :: IO()
main = do
  putStrLn challenge9
  -- Must read the input from a file.

challenge9 = solve Map.empty 0 . map (head) . words $ "5\na\nn\n7\n4\nn\n6\n1\n0\ny\nw\na"
  where
    solve :: Map.Map Char Int -> Int -> String -> String
    solve alpha sumdig [] = "Sum = " ++ (show sumdig) ++ "\n" ++ (unlines . map (\(x,y) -> show x ++ " = " ++ show y) $ Map.toList alpha)
    solve alpha sumdig (x:xs) | Char.isLower x = case Map.lookup x alpha of
                                                   Just n  -> solve (Map.insert x (n+1) alpha) sumdig xs
                                                   Nothing -> solve (Map.insert x 1 alpha) sumdig xs
                              | Char.isDigit x = solve alpha (Char.digitToInt x + sumdig) xs
                              | otherwise      = solve alpha sumdig xs