Yes, that's a fair explanation.
On Tue, Apr 9, 2013 at 7:48 AM, Magicloud Magiclouds < magicloud.magiclo...@gmail.com> wrote: > Thank you for the reply. I've learnt the code of "lines". So it is because > how ByteString works, that the conduit is not a stream of bytes, but > chunks, right? > > > On Tue, Apr 9, 2013 at 12:12 PM, Michael Snoyman <mich...@snoyman.com>wrote: > >> It's a bug in your implementation of takeLine I believe. It doesn't take >> into account that lines can span multiple chunks. When you call takeLine >> the first time, you get "L1\n". leftover puts a chunk with exactly those >> contents back. When you call takeLine the second time, it gets the chunk >> "L1\n", and your splitAt gives you back "L1\n" and "". The "" is then >> leftover, and the next call to takeLine gets it. >> >> Your takeLine needs to include logic saying "there's no newline in this >> chunk at all, let's get the next chunk and try that." You can look at the >> source to lines[1] for an example of the concept. >> >> Michael >> >> [1] >> http://haddocks.fpcomplete.com/fp/7.4.2/20130313-1/conduit/src/Data-Conduit-Binary.html#lines >> >> >> On Mon, Apr 8, 2013 at 8:44 AM, Magicloud Magiclouds < >> magicloud.magiclo...@gmail.com> wrote: >> >>> Say I have code like below. If I comment the leftover in main, I got >>> (Just "L1\n", Just "L2\n", Just "L3\n", Just "L4\n"). But if I did not >>> comment the leftover, then I got (Just "L1\n", Just "L1\n", Just "", Just >>> "L2\n"). >>> Why is not it (Just "L1\n", Just "L1\n", Just "L2\n", Just "L3\n")? >>> >>> takeLine :: (Monad m) => Consumer ByteString m (Maybe ByteString) >>> takeLine = do >>> mBS <- await >>> case mBS of >>> Nothing -> return Nothing >>> Just bs -> >>> case DBS.elemIndex _lf bs of >>> Nothing -> return $ Just bs >>> Just i -> do >>> let (l, ls) = DBS.splitAt (i + 1) bs >>> leftover ls >>> return $ Just l >>> >>> main = do >>> m <- runResourceT $ sourceFile "test.simple" $$ (do >>> a <- takeLine >>> leftover $ fromJust a >>> b <- takeLine >>> c <- takeLine >>> d <- takeLine >>> return (a, b, c, d)) >>> print m >>> >>> -- >>> 竹密岂妨流水过 >>> 山高哪阻野云飞 >>> >>> And for G+, please use magiclouds#gmail.com. >>> >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe@haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >>> >> > > > -- > 竹密岂妨流水过 > 山高哪阻野云飞 > > And for G+, please use magiclouds#gmail.com. >
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