One option is to use pipes-concurrency http://hackage.haskell.org/package/pipes-concurrency. Create http://hackage.haskell.org/package/pipes-concurrency-2.0.3/docs/Pipes-Concur... a mailbox, and pass to *runClient *a callback that reads from the Connection and writes to the mailbox http://hackage.haskell.org/package/pipes-concurrency-2.0.3/docs/Pipes-Concur... . Build http://hackage.haskell.org/package/pipes-concurrency-2.0.3/docs/Pipes-Concur...a *Producer *from the other end of the mailbox and consume it in another thread. Coordinate the threads with something like concurrently http://hackage.haskell.org/package/async-2.0.2/docs/Control-Concurrent-Async... from the async package. On Thursday, October 22, 2015 at 1:42:37 AM UTC+2, Dimitri DeFigueiredo wrote:
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