List recursively all files under the giving path.

gistfile1.hs

import System.Directory

-- For Hugs
(</>) :: FilePath -> FilePath -> FilePath
parent </> child = parent ++ "/" ++ child

fix f = let x = f x in x

when b act = if b then act else return ()


-- Print file and directory recursively

main = fix (\f dir -> getDirectoryContents dir >>= (mapM_ (\d -> putStrLn d >> doesDirectoryExist (dir </> d) >>= flip when (f $ dir </> d))) . filter (`notElem` [".", ".."])) "/tmp"

RecursiveFileList.hs

import Control.Applicative ((<$>))
import System.Directory

-- Because Hugs doesn't have System.FilePath.(</>)
(</>) :: FilePath -> FilePath -> FilePath
parent </> child = parent ++ "/" ++ child

getDirectoryContents' :: FilePath -> IO [FilePath]
getDirectoryContents' dir =
    filter (`notElem` [".", ".."]) <$> getDirectoryContents dir

recursiveFileList :: FilePath -> IO [FilePath]
recursiveFileList path = do
    isDir <- doesDirectoryExist path

    if not isDir
        then do
            isFile <- doesFileExist path
            if isFile
                then return [path]
                else return []
        else do
            subPaths <- map (path </>) <$> getDirectoryContents' path
            subFiles <- mapM recursiveFileList subPaths
            return $ concat subFiles
            -- List files and directories:
            -- return $ path : concat subFiles

main = recursiveFileList "/tmp/oldu/packages" >>= mapM_ putStrLn