I'm using haskell-pipes to recursively traverse a directory and print the files. How do I handle exceptions from the Producer, which is a monad transformer? bracket and handle do not work in this case.
import Control.Exception (handle, SomeException(..))
import Control.Monad (unless)
import System.FilePath.Posix ((</>))
import Pipes
import qualified Pipes.Prelude as P
import System.Posix.Directory (DirStream, openDirStream, closeDirStream, readDirStream)
import System.Posix.Files (getFileStatus, isDirectory)
produceFiles :: DirStream -> Producer FilePath IO ()
produceFiles ds = do
path <- lift $ readDirStream ds
yield path
unless (path == "") $ produceFiles ds
getDC :: FilePath -> Producer FilePath IO ()
getDC top = do
{-
lift $ handle (\(SomeException e) -> putStrLn (show e)) $ do
ds <- openDirStream top
-- DOESN'T WORK: produceFiles ds
-- I would have to "delift" the above somehow.
closeDirStream ds
-}
ds <- lift $ openDirStream top
produceFiles ds
lift $ closeDirStream ds
getDC' :: FilePath -> Producer FilePath IO ()
getDC' top = getDC top >-> P.filter (`notElem` [".", ".."]) >-> P.map (top</>)
getDCR :: FilePath -> Producer FilePath IO ()
getDCR top = for (getDC' top) $ \f -> do
st <- lift $ getFileStatus f
if isDirectory st && f /= top
then getDCR f
else yield f
test top = runEffect $ for (getDCR top) (lift . putStrLn)
main = test "/usr/share"
