Hello All,

I am trying to use both the websockets library and the pipes library. They seem like a natural fit. However, I wanted to use the websockets library to build a pipes 'Producer' and that does not seem possible without some heavy lifting.

The websockets library does not give me a connection I can read from and write to. Instead, I need to supply an IO action (called a clientApp). And execute it using something like:

--runClient :: String       -- ^ Host
--          -> Int          -- ^ Port
--          -> String       -- ^ Path
--          -> ClientApp a  -- ^ Client application -- type ClientApp a = Connection -> IO a
--          -> IO a

main :: IO ()
main = withSocketsDo $ runClient "echo.websocket.org" 80 "/" app

The problem happens when you couple this restriction with the requirement that ClientApps have type 'Connection -> IO a'. Pipes producers are Monad transformer stacks. For example, I would like to build something like:
messageProducer :: Producer' WebsocketMessage IO ()

But this does not run in the IO monad and at the same time I cannot get a 'Connection' object unless I use runClient.

So, it seems I have a catch22 situation. Or have I overlooked something? I'd rather not have to do "un-lifting" on the monad transformer stack.

Has anyone done this before? Any suggestions on how to go about it?


Thanks,


Dimitri