RecursiveContents.hs

module RecursiveContents (getRecursiveContents)
where

import Control.Monad (forM)
import Control.Applicative (liftA2)
import System.Directory (doesDirectoryExist, listDirectory)
import System.FilePath ((</>))

myFilterM :: (Applicative m) => (a -> m Bool) -> [a] -> m ([a],[a])
myFilterM pred = foldr myFilterM' (pure ([],[]))
    where myFilterM' x = liftA2 (
                \flg -> if flg then
                        \(taken,dropped) -> (x:taken,dropped)
                    else
                        \(taken,dropped) -> (taken,x:dropped)
                ) (pred x)

getRecursiveContents :: FilePath -> -- path to root directory
                        IO [FilePath] -- list of found paths
getRecursiveContents root = do
    isDir <- doesDirectoryExist root
    if isDir then do
        contents <- listDirectory root
        seperated <- myFilterM doesDirectoryExist contents
        let dirs = fst seperated
            others = snd seperated
        paths <- forM dirs $ \name -> do
            let path = root </> name
            getRecursiveContents path
        return $ [root </> x | x <- others] ++ concat paths
    else
        return []