wordCount.hs

import Control.Monad
import System.IO
import Data.List
import qualified Data.Map as Map

countWords :: [String] -> Map.Map String Integer
countWords = foldl updateMap Map.empty
  where
    updateMap m word = 
      Map.insert word (1 + (Map.findWithDefault 0 word m)) m
                 
mapToSortedList :: (Ord a) => Map.Map k a -> [(k, a)]
mapToSortedList m = 
  sortBy (\ (_,v1) (_,v2) -> compare v2 v1) (Map.toList m)
  
readLines :: [String] -> IO [String]       
readLines lines = 
  do
    gotEof <- isEOF
    if gotEof 
      then return lines
      else 
      do 
        line <- getLine
        readLines (line : lines)

main :: IO ()
main =
  do
    lines <- readLines []    
    let wordMap = countWords . flatten $ lines in
      forM_ (mapToSortedList wordMap) 
      (\ (k, v) -> putStrLn $ k ++ " " ++ (show v))
    where
      flatten = foldl (\a l -> a ++ words l) []