conduit

问题 I have the following conduit components that are being fused together: awaitVals () :: ConduitT (Element mono) (Element mono) m () intermTmp :: forall o. (Element mono -> Bool) -> ConduitT (Element mono) o m ([Element mono]) The fusion occurs like: awaitVals () .| intermTmp curPred . According to the fuse function ( .| ), I think the types should be OK here. Fuse is: (.|) :: Monad m => ConduitT a b m () -> ConduitT b c m r -> ConduitT a c m r Here's the entire function definition:

问题 I'm getting a strange error when trying to use ResourceT from conduit 1.0.9.1. I'm missing instances from the documentation. For example import Control.Monad import Control.Monad.Trans import Control.Monad.IO.Class import Data.Conduit test = runResourceT (lift $ print "Hello world") fails with No instance for ( MonadTrans ResourceT ) arising from a use of lift , although there are many instances in the docs, including MonadTrans ResourceT . Checking REPL confirms the problem: Prelude> :m Data

问题 I'm getting a strange error when trying to use ResourceT from conduit 1.0.9.1. I'm missing instances from the documentation. For example import Control.Monad import Control.Monad.Trans import Control.Monad.IO.Class import Data.Conduit test = runResourceT (lift $ print "Hello world") fails with No instance for ( MonadTrans ResourceT ) arising from a use of lift , although there are many instances in the docs, including MonadTrans ResourceT . Checking REPL confirms the problem: Prelude> :m Data

问题 I have a simple task - read a bunch of lines out of a file and do something with each one of them. Except the first one - which are some headings to be ignored. So I thought I'd try out conduits. printFile src = runResourceT $ CB.sourceFile src =$= CT.decode CT.utf8 =$= CT.lines =$= CL.mapM_ putStrLn Cool. So now I just want to drop the first line off ... and there seems to be a function for that - printFile src = runResourceT $ CB.sourceFile src =$= CT.decode CT.utf8 =$= CT.lines =$= drop 1

问题 I'm trying to understand the differences between conduit and pipes . Unlike pipes , conduit has the concept of leftovers. What are leftovers useful for? I'd like to see some examples where leftovers are essential. And since pipes don't have the concept of leftovers, is there any way to achieve a similar behavior with them? 回答1: Gabriel's point that leftovers are always part of parsing is interesting. I'm not sure I would agree, but that may just depend on the definition of parsing. There are

问题 I don't know why my code breaks. At first I thought it was because parseURL gives [] for the requestHeaders . Okay, so maybe I just need to tell it what the resquestHeaders should be. Well, I examined the requestHeaders generated from my old, working code. It too, returns a [] . So now I am out of ideas. Below is the old working code, followed my things I have been trying in GHCi with with new conduits based library. captureRawJson :: IO Response captureRawJson = do nManager <- newManager

问题 I am trying to construct a Conduit that receives as input ByteString s (of around 1kb per chunk in size) and produces as output concatenated ByteString s of 512kb chunks. This seems like it should be simple to do, but I'm having a lot of trouble, most of the strategies I've tried using have only succeeded in dividing the chunks into smaller chunks, I haven't succeeded in concatenating larger chunks. I started out trying isolate , then takeExactlyE and eventually conduitVector , but to no

问题 I've been struggling with this problem for a while now, though to be fair, I've learned a lot about Conduit, since previously I was mostly using canned examples with a few exceptions. The basic problem is framed like this for conduits A , B , and C ; A .| B ( A feeds into B ) and A .| C , and finally I need to have a function that takes B and C and produces an intermediate Conduit, call it Merge B C , so that I can do (Merge B C) .| D . My experience in non Haskell languages with FRP

问题 I'm reading from a file using sourceFile , but I also need to introduce randomness into the processing operation. The best approach I believe is to have a producer that is of the type Producer m (StdGen, ByteString) where StdGen is used to generate the random number. I'm intending for the producer to perform the task of sourceFile, as well as producing a new seed to yield everytime it sends data downstream. My problem is, there doesn't seem to be a source-combiner like zipSink for sinks.

问题 Let's assume we create the file a.txt.gz as follows: $ echo "foobar" > a.txt $ gzip a.txt I intend to use zlib-conduit in order to emulate zcat in Haskell. I'm looking for a simple example that can also be applied to bzlib-conduit. Note: This question was answered immediately in a Q&A-Style. Therefore it intentionally does not show any research effort. 回答1: If you intend to work with conduit s, I highly recommend to read the excellent Conduit overview by Michael Snoyman and the FP Complete