On 02/01/2013 05:21 AM, Michael Snoyman wrote:

Firstly, what's the use case that you want to deal with lists? If it's for efficiency, you'd probably be better off using a Vector instead.

That is a good point, and I wanted to go that way, but was not sure it would help me a lot here. My use case is for services where there is a "bulk" API, such as Redis pipelining or Elasticsearch bulk inserts. The network round-trip gains would exceed by far those from a List to Vector conversion.

But I think the inverse of `concat` is `singleton = Data.Conduit.List.map return`, or `awaitForever $ yield . return`, using the list instance for Monad. Your conduitMap could be implemented then as:

conduitMap conduit = concat =$= conduit =$= singleton

I can see how to do singleton, but that would gain me ... singletons. That means I could not exploit a bulk API.

On 01/02/2013 08:21, Michael Snoyman wrote:

So you're saying you want to keep the same grouping that you had originally? Or do you want to batch up a certain number of results? There are lots of ways of approaching this problem, and the types don't imply nearly enough to determine what you're hoping to achieve here.

Sorry for not being clear. I would like to group them "as much as possible", that is up to a certain limit, and also within a "time threshold". I believe that the conduit code will be called only when something happens in the conduit, so an actual timer would be useless (unless I handle this at the source perhaps, and propagate "ticks"). That is why in my first message I talked about stacking things into the list until the conduit has no more input available, or a maximum size is reached, but was not sure this even made sense.

I think this is probably the right approach. However, there's something important to point out: flushing based on timing issues must be handled *outside* of the conduit functionality, since by design conduit will not allow you to (for example) run `await` for up to a certain amount of time. You'll probably need to do this outside of your conduit chain, in the initial Source. It might look something like this: yourSource = do mx <- timeout somePeriod myAction yield $ maybe Flush Chunk mx yourSource On Sun, Feb 3, 2013 at 5:06 PM, Felipe Almeida Lessa

wrote:

I guess you could use the Flush datatype [1] depending on how your data is generated.

Cheers,

[1] http://hackage.haskell.org/packages/archive/conduit/0.5.4.1/doc/html/Data-Co...

On Fri, Feb 1, 2013 at 6:28 AM, Simon Marechal wrote:

...

On 01/02/2013 08:21, Michael Snoyman wrote:

...

So you're saying you want to keep the same grouping that you had originally? Or do you want to batch up a certain number of results? There are lots of ways of approaching this problem, and the types don't imply nearly enough to determine what you're hoping to achieve here.

Sorry for not being clear. I would like to group them "as much as possible", that is up to a certain limit, and also within a "time threshold". I believe that the conduit code will be called only when something happens in the conduit, so an actual timer would be useless (unless I handle this at the source perhaps, and propagate "ticks").

That is why in my first message I talked about stacking things into the list until the conduit has no more input available, or a maximum size is reached, but was not sure this even made sense.

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-- Felipe.

Hmm, that's an interesting trick. I can't say that I ever thought bracketP would be used in that way. The only change I might recommend is using addCleanup[1] instead, which doesn't introduce the MonadResource constraint. Michael [1] http://haddocks.fpcomplete.com/fp/7.4.2/2012-12-11/conduit/Data-Conduit-Inte... On Mon, Feb 4, 2013 at 4:37 PM, Kevin Quick wrote:

While on the subject of conduits and timing, I'm using the following conduit to add elapsed timing information:

timedConduit :: MonadResource m => forall l o u . Pipe l o o u m (u, NominalDiffTime) timedConduit = bracketP getCurrentTime (\_ -> return ()) inner where inner st = do r <- awaitE case r of Right x -> yield x >> inner st Left r -> deltaTime st >>= \t -> return (r,t) deltaTime st = liftIO $ flip diffUTCTime st <$> getCurrentTime

I'm aware that this is primarily timing the downstream (and ultimately the Sink) more than the upstream, and I'm using the bracketP to attempt to delay the acquisition of the initial time (st) until the first downstream request for data.

I would appreciate any other insights regarding concerns, issues, or oddities that I might encounter with the above.

Thanks, Kevin

On Mon, 04 Feb 2013 02:25:11 -0700, Michael Snoyman wrote:

I think this is probably the right approach. However, there's something

...

important to point out: flushing based on timing issues must be handled *outside* of the conduit functionality, since by design conduit will not allow you to (for example) run `await` for up to a certain amount of time. You'll probably need to do this outside of your conduit chain, in the initial Source. It might look something like this:

yourSource = do mx <- timeout somePeriod myAction yield $ maybe Flush Chunk mx yourSource

On Sun, Feb 3, 2013 at 5:06 PM, Felipe Almeida Lessa < felipe.lessa@gmail.com

...

wrote:

I guess you could use the Flush datatype [1] depending on how your

...

data is generated.

Cheers,

[1] http://hackage.haskell.org/**packages/archive/conduit/0.5.** 4.1/doc/html/Data-Conduit.**html#t:Flushhttp://hackage.haskell.org/packages/archive/conduit/0.5.4.1/doc/html/Data-Co...

On Fri, Feb 1, 2013 at 6:28 AM, Simon Marechal wrote:

...

On 01/02/2013 08:21, Michael Snoyman wrote:

...

So you're saying you want to keep the same grouping that you had originally? Or do you want to batch up a certain number of results? There are lots of ways of approaching this problem, and the types don't imply nearly enough to determine what you're hoping to achieve here.

Sorry for not being clear. I would like to group them "as much as possible", that is up to a certain limit, and also within a "time threshold". I believe that the conduit code will be called only when something happens in the conduit, so an actual timer would be useless (unless I handle this at the source perhaps, and propagate "ticks").

That is why in my first message I talked about stacking things into the list until the conduit has no more input available, or a maximum size is reached, but was not sure this even made sense.

______________________________**_________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://www.haskell.org/mailman/listinfo/haskell-cafe

-- Felipe.

-- -KQ

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On Mon, Feb 4, 2013 at 3:47 PM, Simon Marechal wrote:

On 03/02/2013 16:06, Felipe Almeida Lessa wrote:

...

I guess you could use the Flush datatype [1] depending on how your data is generated.

Thank you for this suggestion. I tried to do exactly this by modifying my bulk Redis source so that it can timeout and send empty lists [1]. Then I wrote a few helpers conduits[2], such as :

concatFlush :: (Monad m) => Integer -> Conduit [a] m (Flush a)

which will convert a stream of [a] into a stream of (Flush a), sending Flush whenever it encounters and empty list or it send a tunable amount of data downstream.

I finally modified my examples [3]. I realized then it would be nice to have fmap for conduits (but I am not sure how to write such a type signature). Suggestions are welcome !

Actually `fmap` already exists on the Pipe datatype, it just probably doesn't do what you want. It modifies the return value, which is only relevant for Sinks. What you probably are looking for is mapOutput[1]. Michael [1] https://haskell.fpcomplete.com/hoogle?q=mapOutput

[1]

https://github.com/bartavelle/hslogstash/commit/663bf8f5e6058b476c9ed9b5c9cf... [2] https://github.com/bartavelle/hslogstash/blob/master/Data/Conduit/Misc.hs [3]

https://github.com/bartavelle/hslogstash/blob/master/examples/RedisToElastic...