In Haskell, how do I promptly close resources?

Question

Old pipes tutorial has following example. How would this code look like with version 4.1.1?

  read' :: FilePath -> Frame Text IO C C ()
  read' file = do
      liftU $ putStrLn "Opening file..."
      h <- liftU $ openFile file ReadMode
      -- The following requires "import qualified Control.Monad as M"
      finallyD (putStrLn "Closing file ..." M.>> hClose h) $ readFile' h

score 2 · Accepted Answer · answered Apr 20 '14 at 04:29

The equivalent function is readFile from Pipes.Safe.Prelude, which you can find here. I've pasted the source below for reference:

withFile :: MonadSafe m => FilePath -> IO.IOMode -> (IO.Handle -> m r) -> m r
withFile file ioMode = bracket (liftIO $ IO.openFile file ioMode) (liftIO . IO.hClose)

readFile :: MonadSafe m => FilePath -> Producer' String m ()
readFile file = withFile file IO.ReadMode P.fromHandle

In Haskell, how do I promptly close resources?

1 Answers1