CountWords.hs

import qualified Data.Map.Strict as M
import Data.List (foldl', sortOn)

-- functors and bind to the rescue!
main :: IO ()
main = fmap countWords getContents >>= putStrLn . show


countWords :: String -> [(String,Integer)]
countWords =  sortOn snd . M.toList . foldl' (\m w -> M.insertWith (+) w 1 m) M.empty  . words


-- in one line if you really want, though I think it's too long if we're being honest
alternativeMain :: IO ()
alternativeMain = fmap (sortOn snd . M.toList . foldl' (\m w -> M.insertWith (+) w 1 m) M.empty  . words)  getContents >>= putStrLn . show