ws.hs

--
-- wc.hs: word count
--
-- Given a file name in the first command line argument,
-- print WORD: COUNT for each WORD per line.
-- The output is ordred by COUNT.
--

import System
import Data.List
import Data.Function

count :: [String] -> [(String, Int)]
count line = map count' $ group $ sort line
    where count' xs = (head xs, length xs)

sortedCount :: [String] -> [(String, Int)]
sortedCount line = sortBy (compare `on` snd) $ count line

main = do
    args <- getArgs
    content <- readFile (head args)
    let inputWords = concat $ map words $ lines content
    let results = [w ++ ": " ++ show n | (w, n) <- sortedCount inputWords]
    sequence_ (map putStrLn results)