Hello, I am writing a software which do some data treatement from hdf5 files. In order to access the data which are stored in arrays, I need to open and closes ressources. This is the purpose of the withHdf5PathP function. given a file f and a UhvPath I end up with this withUhvPathP :: (MonadSafe m, Location l) => l -> UhvPath -> ((Int -> IO Geometry) -> m r) -> m r withUhvPathP f (UhvPath m o d g w) gg = withHdf5PathP f m $ \m' -> withHdf5PathP f o $ \o' -> withHdf5PathP f d $ \d'-> withHdf5PathP f g $ \g' -> withHdf5PathP f w $ \w' -> gg (\j -> do mu <- get_position m' j omega <- get_position o' j delta <- get_position d' j gamma' <- get_position g' j wavelength <- getValueWithUnit w' 0 angstrom let positions = Data.Vector.Storable.fromList [mu, omega, delta, gamma'] let source = Source wavelength pure $ Geometry Uhv source positions Nothing) then I use this like this forever $ do (Chunk fp from to) <- await withFileP (openH5 fp) $ \f -> withHdf5PathP f imgs $ \dimgs -> withUhvPathP f dif $ \getDiffractometer -> withSamplePathP f samp $ \getSample -> forM_ [from..to-1] (\j -> yield =<< liftIO (DataFrameHkl <$> pure j <*> get_image' det dimgs j <*> getDiffractometer j <*> getSample j)) so once I open the resources, I use the getDiffratometer ((Int -> IO Geometry) -> m r) function give the position on the stream and it return the value at the j position. the purpose of this is to open the ressources only once at the begining and then send the values in a Pipe via the yield function of pipes package. I hope, I was clear. 1) I find the withUhvPathP sort of ugly, and I would like to know if it could be written more elegantly, because I will need to write a lot's of these function for different types. 2) It is the right way to design a solution to my problem (open ressources and send each values into a stream). thanks for you attention. Frederic