On Fri, Feb 10, 2012 at 4:26 PM, Alexander V Vershilov
Hello, cafe!
I have somq questions about proper conduit usage in some usecases, I can't find a good way to solve this problems
1). adding additional source to conduit processing [1] Sometimes I want to run a Source and send use it to produce output e.g. have something like:
runSource :: ResourceT m => a -> Source m b runSource = undefined
test1 :: ResourceT m => Conduit a m b test1 = Conduit push close where push = runSource close = undefined -- In my first problem I've got -- push i = case i of Left _ -> oneValue ; Right -> runSource -- but it can be solved with oneValue = sourceList [oneValue]
We have a `sequenceSink` function that takes a `Sink` and turns it into a `Conduit` by running it repeatedly. It looks to me like the best approach would be to have an equivalent `sequenceSource`, something like: sequenceSource :: (a -> Source m b) -> Conduit a m b I can help out with implementation.
2). pushing data back [1]
e.g. I have
test2 :: ResourceT Conduit ByteString m b test2 = Conduit push close where conduit i = let (item,lft) = parse i in -- I want to send lft back to test2 and -- process item -- in the other case I want to be able to send data back to -- previous or arbitrary level, e.g. test1 $= test2 $= test3 ^--------| (<<<=) lft
This is purposely not allowed currently, for various low-level reasons. I can get into details if anyone's curious, but don't have time at the moment.
3). split stream to send it to different Sinks, e.g.
sendToAll test3 [sink1,sink2,sink3]
It's mostly straight-forward to implement, but there are some questions. In particular: what do you do if sink1 terminates earlier than sink2? Do you call sinkClose on sink2, or continue pulling data until all of the sinks close? Also, I think it could be a Sink, e.g.: sendToAll :: [Sink a m b] -> Sink a m [b]
4). send additional data from the other place, e.g.
src $= handle $$ snk -- state -^ -- I want to send message into handle to change it's state -- It can be done with stm-conduit and Either (Left for commands -- and Right for data), but it seems its overkill
I'm not sure what you're looking for here. You want to control the behavior of src from snk? If you just want to modify the handle from snk, you could pass the handle to snk directly. Michael