import System.IO
import System.Posix
import System.Directory

show_current_dir :: IO ()
show_current_dir = do
  curr_dir <- getWorkingDirectory


  putStrLn ("Current Working Directory:" ++ curr_dir)

ls_dir1 :: String -> IO [()]
ls_dir1 fp = do
  files <- getDirectoryContents fp
  putStrLn ("ls_dir1: Files in " ++ fp ++ ":")


  mapM putStrLn files

read_fp_from_DirStream :: DirStream -> IO()
read_fp_from_DirStream dp = do
  f <- readDirStream dp
  if f == "" then return () else do putStrLn f
                                    read_fp_from_DirStream dp


ls_dir2 :: String -> IO ()
ls_dir2 fp = do
  dp <- openDirStream fp
  putStrLn ("ls_dir2: files in " ++ fp ++ ":")
  read_fp_from_DirStream dp
  closeDirStream dp


main :: IO ()
main = do
  putStrLn "Unix programming use Haskell"
  show_current_dir
  ls_dir1 "/"
   ls_dir2 "/home"