Maciej Piechotka writes:

Hello.

I've tried to combine lazy IO and parsec. The hole process is done by network.

Currently I have implemented 'short parsers' so I enter them on need. To update state I have following code: parser2nntp :: Monad m => NntpParser m a -> NntpT m a parser2nntp p = do s <- NntpT (gets $ input . connection) e <- runParserT (do v <- p i <- getInput return (v, i)) () "" s case e of Left er -> error $ show er Right (v, i') -> (NntpT (modify (pNI i')) >> return v) where pNI :: Monad m => ByteString ->NntpState m -> NntpState m pNI i s = s {connection = (connection s) {input = i}}

However the 4 line (i <- getInput) blocks the execution as trace indicated. String returned have no input available so it should block on evaluation - and here I pass only a reference to it (or rather I think so). What's wrong?

PS. Full code is in darsc nntp repository http://code.haskell.org/nntp/ - please note that it seems to require network compiled against parsec 3 - not 2.

This code seems to work: parser2nntp :: Monad m => NntpParser m a -> NntpT m a parser2nntp p = do s <- NntpT (gets $ input . connection) r <- parserRep =<< runParsecT p (State s (initialPos "") ()) case r of Ok v (State i _ _) _ -> NntpT (modify $ pNI i) >> return v Error e -> error $ show e where parserRep (Consumed x) = x parserRep (Empty x) = x pNI i s = s {connection = (connection s) {input = i}} Regards