2012/2/3 Michael Snoyman <mich...@snoyman.com> > 2012/2/3 Ertugrul Söylemez <e...@ertes.de>: > > Hello there, > > > > I'm trying to build a server for testing the conduit and network-conduit > > packages. As a contrived example the goal is to pick the first three > > lines from the client and send them back without the line feeds. After > > that, I'd like to switch to a simple echo server. This is the code: > > > > module Main where > > > > import Data.Conduit > > import Data.Conduit.Binary as Cb > > import Data.Conduit.List as Cl > > import Data.Conduit.Network > > > > handleClient :: Application > > handleClient src snk = > > src $$ do > > (Cb.lines =$= Cl.isolate 3) =$ snk > > snk > > > > main :: IO () > > main = runTCPServer (ServerSettings 4000 Nothing) handleClient > > > > I'm not sure whether it is correct to use the 'snk' sink multiple times, > > and intuitively I'd say that this is wrong. What would be the proper > > way to do this? > > > > > > Greets, > > Ertugrul > > In this particular case, it will work due to the implementation of > snk. In general, however, you're correct: you should not use the same > sink twice. >
Since Sink works in a CPS fashion, by which i mean every step it return a new push close pair, i think it can be used multiple time. > > I haven't thought about it much yet, but my initial recommendation > would be to create a new Conduit using SequencedSink, which takes the > three lines and then switches over to a passthrough conduit. The > result looks like this: > > > module Main where > > import Data.Conduit > import Data.Conduit.Binary as Cb > import Data.Conduit.List as Cl > import Data.Conduit.Network > > handleClient :: Application > handleClient src snk = src $$ myConduit =$ snk > > main :: IO () > main = runTCPServer (ServerSettings 4000 Nothing) handleClient > > myConduit = > sequenceSink 3 go > where > go 0 = return $ StartConduit $ Cl.map id > go count = do > mx <- Cb.lines =$ Cl.head > case mx of > Nothing -> return Stop > Just x -> return $ Emit (count - 1) [x] > > Michael > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- http://www.yi-programmer.com/blog/
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