On Thu, Jun 9, 2011 at 4:04 PM, Alexander V Vershilov wrote:

Hello.

Thu, Jun 09, 2011 at 01:40:51PM -0500, Antoine Latter wrote

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On Thu, Jun 9, 2011 at 3:14 PM, Alexander V Vershilov wrote:

...

Hello.

I'm writing a small tcp server with that can handle connections and answer by rules writen in a small script that can be interpreted by server. For this purpose I've written an interpreter that has type

 ErrorT MyError (StateT ScriptState IO)

so I can call "native" IO function in that script, and define new one.  I can run this script with runState (runErrorT (...)) oldState.

But there is one problem: in script i should be able to call functions that will stop script interpretation and wait for some server event. To continue interpretation.

What do you mean by 'server event'? How do you plan on representing these events?

I'm using term server event for next thing when server get some message from client it generate 'server event' i.e. some action or save this event in event queue. And then forces this queue to act.

So simplified workflow looks like:  client                 server                             interpretator 1 *sends some messages -> save parsed messages in queue 2 *send 'END' message  -> forces functions F(message) from                          queue 3                        *some F is to call interpretator  -> run script 4                                                          <-  *call server                         <- send messages to client           callback                         goto step 2                       <- *finish script

* - stand for event initiator. Here everything can be done in a straitforward way.

What I want to do and do know a good way for: client        server          -> run script                                ...                             <- call 'wait' command          <-> *goto 1 ... send 'END' -> continue script ->

Sorry if I do not answer on your question directly.

-- Best regards,  Alexander V Vershilov

The next question - are you waiting for the client to open a new connection to your server and send the result, or are you waiting for the client to send a response on an already open socket? If the later, the GHC IO manager will halt your thread of execution and wake it back up once the socket has data on it. If the former, you'll need to explore some of the solutions Heinrich has put forth.

...

...

Can smb give an advice what is the best way to do it?

-- Best regards  Alexander V Vershilov

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Just for the culture (because Heinrich's solution is undoubtly simpler) you can also achive this using continuations. This is one of the purposes of the Cont monad, used jointly with a State monad, you can store the continuations and resume them later. 2011/6/10 Heinrich Apfelmus

Alexander V Vershilov wrote:

...

I'm writing a small tcp server with that can handle connections and answer by rules writen in a small script that can be interpreted by server. For this purpose I've written an interpreter that has type

ErrorT MyError (StateT ScriptState IO)

so I can call "native" IO function in that script, and define new one. I can run this script with runState (runErrorT (...)) oldState.

But there is one problem: in script i should be able to call functions that will stop script interpretation and wait for some server event. To continue interpretation. Can smb give an advice what is the best way to do it?

Basically, you want to stop the interpreter and resume it at some later point. You need to implement a custom monad for that, which can easily be done with the help of my operational package.

http://projects.haskell.org/operational/

In particular, the examples

WebSessionState.lhs TicTacToe.hs PoorMansConcurrency.hs

show how to suspend and resume the control flow. Feel free to request additional examples.

Best regards, Heinrich Apfelmus

-- http://apfelmus.nfshost.com

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