45 listAll :: FilePath -> IO [FilePath]
 46 listAll f = do
 47     isFile <- doesFileExist f
 48     if isFile then
 49         return [f]
 50     else
 51         do
 52             fs <- getDirectoryContents f
 53             let files = fmap (f </>) . filter ((/='.') . head) $ fs
 54             branches <- forM files listAll
 55             return $ concat branches