ナンバリング ref: http://qiita.com/items/d325823f141375816cf5

numbering.hs

module Main where
import System.Environment

main :: IO ()
main = mapM_ numbering =<< getArgs

numbering :: FilePath -> IO ()
numbering f = putStr . unlines . zipWith number [1..] . lines =<< readFile f

number :: Int -> String -> String
number n l = rjustify 6 (show n) ++ ": " ++ l
  where
    rjustify w = reverse . take w . (++ repeat ' ') . reverse