[Haskell-cafe] happstack simpleHTTP & state monad

[Corentin Dupont]

Hi Erik,
yes you're right, I'm experimenting with an IORef now (a TVar would be a
better idea).
I also tried the idea expressed here, to keep the state:
https://groups.google.com/forum/?fromgroups=#!msg/happs/_JSpaJKub0k/oa0K01IBlh0J
But without success so far. The server is returning me the state in the
Response type but I cannot manage to reinject it for the next call :)

Best,
Corentin

On Thu, Aug 30, 2012 at 9:47 PM, Erik Hesselink <hesselink at gmail.com> wrote:

> The way you wrote it, you run the state transformer once for each
> request. So the state will be available within a single request, but
> not between requests. If you want to persist state between requests,
> you can use one the the mutable variables available (TVar or MVar are
> good choices; IORefs also work, but you have to take care about
> concurrency, using e.g. atomicModifyIORef). Create them before calling
> simpleHTTP, then pass them in to use them in your handler. You can put
> them in a ReaderT to avoid passing them, if you want.
>
> Another choice is to use something like a database or the file system
> for persistent state. Databases usually handle most concurrency
> problems for you, while file systems don't.
>
> Regards,
>
> Erik
>
> On Thu, Aug 30, 2012 at 7:29 PM, Corentin Dupont
> <corentin.dupont at gmail.com> wrote:
> > Hi all,
> > I'm trying to make a web server that manages its own state. The user can
> > issue commands that modifies the state.
> > I did like below but unfortunatly the state is not keep after a command
> is
> > issued...
> > What is the right way to do it? Is there any example sites with an
> internal
> > state with happstack?
> >
> > data Game = (the state of my game)
> > type NomicServer             = ServerPartT (StateT Game IO)
> >
> > launchWebServer :: Game -> IO ()
> > launchWebServer initialState = do
> >    putStrLn "Starting web server...\nTo connect, drive your browser to
> > \"http://localhost:8000/Login\""
> >    d <- getDataDir
> >    simpleHTTP' unpackStateT nullConf $ server d
> >
> >
> > server :: FilePath -> ServerPartT (StateT Game IO) Response
> > server d sh = mconcat [fileServe [] d, do
> >                                    decodeBody (defaultBodyPolicy "/tmp/"
> > 4096 4096 4096)
> >                                    html <- implSite "
> http://localhost:8000/"
> > "" nomicSite
> >                                    return $ toResponse html]
> >
> > unpackStateT:: Game -> UnWebT (StateT Game IO) Response -> UnWebT IO
> > Response
> > unpackStateT g w = evalStateT w g
> >
> > --handler for web routes
> > nomicSite :: Site PlayerCommand (NomicServer Html)
> > nomicSite = setDefault (Noop 0) Site {
> >       handleSite         = \f url -> unRouteT (routedNomicCommands url) f
> >     , formatPathSegments = \u -> (toPathSegments u, [])
> >     , parsePathSegments  = parseSegments fromPathSegments
> > }
> >
> > Thanks a lot,
> > Corentin
> > _______________________________________________
> > Haskell-Cafe mailing list
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> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
>
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