Translate directory tree to a tree

gistfile1.txt

data Tree a = Leaf a | Node a [Tree a]

scanDir :: String -> IO (Tree String)
scanDir path = do
  contents <- getDirectoryContents path `catch` const (return [])
  let files = sort . filter (`notElem` [".", ".."]) $ contents
  let pathsAndFiles = zip (repeat path) files
  tree <- forM pathsAndFiles $ \(path, file) -> do
    isDirectory <- doesDirectoryExist path
    if isDirectory
      then Node file (scanDir path++file)
      else Leaf file
  return tree