[Haskell-cafe] how to create a pipes producer from websockets?

[John Lenz]

The yesod-websockets library has a conduit api on top of websockets which I
use, so I have conduits processing messages.  Conduit and pipes work
similarly, so I suspect the technique from yesod-websockets will work fine
for pipes, just look at the yesod-websockets source code:

https://hackage.haskell.org/package/yesod-websockets-0.2.3/docs/Yesod-WebSockets.html

On Wed, Oct 21, 2015 at 6:42 PM, Dimitri DeFigueiredo <
defigueiredo at ucdavis.edu> 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
>
>
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20151021/9c6c48d9/attachment.html>