withSinkFile and a lot of other with* functions doesn't necessarily need a MonadUnliftIO instance of the underlying monad

[poscat0x04]

The current implementation of withSinkFile is:

withSinkFile
  :: (MonadUnliftIO m, MonadIO n)
  => FilePath
  -> (ConduitM ByteString o n () -> m a)
  -> m a
withSinkFile fp inner =
  withRunInIO $ \run ->
  IO.withBinaryFile fp IO.WriteMode $
  run . inner . sinkHandle

which requires the underlying monad to have a MonadUnliftIO instance. But it is enough to implement withSinkFile with only a MonadMask, which is a strictly weaker constraint than MonadUnliftIO:

withSinkFile :: (MonadMask m, MonadIO m, MonadIO n) => FilePath -> (ConduitT ByteString o n () -> m a) -> m a
withSinkFile fp k =
  bracket
    (liftIO . openBinaryFile WriteMode)
    (liftIO . hClose)
    (k . sinkHandle)

This is also true for a lot of other with* functions. It would be nice to loosen the constraints on these functions.

[snoyberg]

I'm not in favor of recommending MonadMask, which favors complicated and unnecessary monad stacks. Making a change like that would additionally be backwards incompatible.

…

On Wed, Jan 6, 2021 at 1:30 PM Poscat ***@***.***> wrote: The current implementation of withSinkFile is: withSinkFile :: (MonadUnliftIO m, MonadIO n) => FilePath -> (ConduitM ByteString o n () -> m a) -> m a withSinkFile fp inner = withRunInIO $ \run -> IO.withBinaryFile fp IO.WriteMode $ run . inner . sinkHandle which requires the underlying monad to have a MonadUnliftIO instance. But it is enough to implement withSinkFile with only a MonadMask, which is a strictly weaker constraint than MonadUnliftIO: withSinkFile :: (MonadMask m, MonadIO m, MonadIO n) => FilePath -> (ConduitT ByteString o n () -> m a) -> m a withSinkFile fp k = bracket (liftIO . openBinaryFile WriteMode) (liftIO . hClose) (k . sinkHandle) This is also true for a lot of other with* functions. It would be nice to loosen the constraints on these functions. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#458>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAMCB3YQKWQNOK74B3V7JLSYRCVVANCNFSM4VXNAGNA> .