Pre/post processing in Effect handler

[emlautarom1]

Assume that I have the following Effect:

data Severity = Info | Error | Fatal
  deriving (Show, Eq, Ord, Bounded)

data Logger e :: Effect where
  Log :: Severity -> String -> (Logger e) m ()

type instance DispatchOf (Logger e) = Dynamic

log :: (Logger e :> es) => Severity -> String -> Eff es ()
log severity message = send $ Log severity message

I would like to write an interpreter that:

1. Takes a FilePath as argument
2. Opens the file in WriteMode once
3. Every 10 writes it flushes the file handle

(this is just an example use case, not something real)

As a skeleton I have something like:

runFileLogger :: (IOE :> es) => FilePath -> Eff (Logger e : es) a -> Eff es a
runFileLogger path = do
  -- Use `withFile` or similar to get a `Handle`. The file should be opened once.
  -- withFile path WriteMode $ \handle ->
  -- Store some kind of counter variable (`IORef` maybe?)
  -- counter <- ???
  interpret $ \env op -> case op of
    Log severity message -> do
      -- update the counter
      liftIO $ hPutStrLn handle message
      -- if the counter reaches 10, call `hFlush handle`

1. The signature runFileLogger :: (IOE :> es) => FilePath -> Eff (Logger e : es) a -> Eff es a is what I would like to have.
2. Notice how certain operations should be executed "before" the interpret call
3. We're dealing with the withXXX pattern since we want to do something before & after interpreting the Effect: open the file and closing it.

[emlautarom1]

After some trial and error I ended up with:

runFileLogger :: (IOE :> es) => FilePath -> Eff (Logger e : es) a -> Eff es a
runFileLogger path logger = do
  counter <- liftIO $ newIORef (0 :: Int)
  withFile path WriteMode $ \handle -> do
    interpretWith logger $ \_ -> \case
      Log severity message -> liftIO $ do
        atomicModifyIORef' counter $ \c -> (c + 1, ())
        hPutStrLn handle message
        whenM ((== 10) <$> readIORef counter) $ do
          hFlush handle
          atomicModifyIORef' counter $ const (0, ())

This is pretty much what I was looking for but there are a couple of issues:

1. This requires unliftio as a dependency to workaround the IO limitation of System.IO.withFile.
2. There are several usages of liftIO scattered throughout the implementation.

These are very small issues but I would like to know if there is any way to remove them.