import Control Monad import System Directory import System FilePath im

import Control.Monad
import System.Directory
import System.FilePath
import System.Environment

concatMapM f xs = liftM concat (mapM f xs)

hier dir = do
    subdirs <- getDirectoryContents dir >>= return . filter (`notElem` [".", ".."])
    lines <- filterM doesDirectoryExist (map (dir </>) subdirs) >>= concatMapM hier
    return $ dir : map ("  " ++) lines

main = do
    dir:_ <- getArgs
    hier dir >>= putStr . unlines