[Haskell-cafe] How to design an network client with user program.

[Michael Snoyman]

It doesn't seem like you're trying to perform multiple actions
simultaneously. For example, you don't need to be able to read from the
server and send data back at the same time. Instead, you'll have a single
thread of execution. Am I right?

If so, it seems like the simplest thing would be for you to allow users to
write something like:

    Conduit MsgFromServer m MsgToServer

Assuming you had conduits to convert an incoming byte stream to a stream of
MsgFromServer and the equivalent for sending, you'd end up with something
like:

    appSource appData $$ toMsgFromServer =$ clientSuppliedConduit =$
fromMsgToServer =$ appSink appData

Michael


On Tue, Apr 9, 2013 at 1:09 PM, Alexander V Vershilov <
alexander.vershilov at gmail.com> wrote:

>
> Hello.
>
> I have next problem: I have a network client that connects to server,
> listens for messages and generate responces. So the control flow can be
> represended as:
>
> server -- input -> {generate output} -> output
>
> Output can be generated using default implementation or can overriden by
> user.
>
> The main difficulty appeares when I need to add a user program on the top
> of this logic,
> i.e. from user-side I want to have dsl:smth like
>
> withClient $ do
>    x <- send message
>    waitFor x
>    timeout 5000000
>    forever $ sendRandomMessage
>
> i.e. an ability to send messages, waiting for some event (message to
> come), waiting for
> timeout.
>
> The question is how to define such logic without a big overhead. I see a
> solution using conduit, it's possible to create 3 processes: listener,
> user, sender.
>
>                          +----> user ----+
>                          |                    |
> -input -> listener +----------------->+---- sender ->
>
> and use TQueue or TChan to send messages between them, however there can
> be another possible solutions, that uses less resources, or another design.
>
>
> --
> Alexander
>
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