For the benefit of others, the definition of `draw10` would look like this:
draw10 = zoom (splitAt 10) drawAll
I think a way to simplify this further and remove the intermediate list
would be to define a function of type:
foldAll :: (Monad m) => L.Fold a b -> Parser a m b
Then you could simplify this further to:
loop = do
(avgTemp, avgHumidity) <- zoom (splitAt 10) (foldAll averages)
...
This would also improve memory usage because you wouldn't need to bring
the intermediate list into memory.
I just added this to the `lenses` branch of `pipes-parse` as `foldAll`
and `foldMAll`, so give that a try and see if that works for you. These
don't use the `Fold` type but you can unpack any `Fold`'s arguments and
pass it to these. Here's some example usage:
import Control.Monad.Trans.State.Strict
import Lens.Family.State.Strict
import Pipes
import Pipes.Parse
import Prelude hiding (splitAt)
sum10 :: (Monad m) => Parser Double m Double
sum10 = zoom (splitAt 10) (foldAll (+) 0 id)
main = print $ evalState sum10 (each [1..])
-- prints 55
On 12/19/2013 12:24 PM, Pierre R wrote:
This is actually getting easier with the new API:
loop = do
records <- draw10
let (avgTemp, avgHumidity) = L.fold averages records
liftIO $ printf "-- Report: average temperature is %d°C,
average humidity is %d%% \n" avgTemp avgHumidity
eof <- PP.isEndOfInput
unless eof loop
Cheers,
On Wednesday, December 18, 2013 9:29:32 PM UTC+1, Pierre R wrote:
Hi,
I am having a go with the new parsing API (just for learning
purposes). How should I convert the following code ?
(avgTemp, avgHum) <- fold' averages (input >-> P.take 10)
https://github.com/PierreR/pipes-zmq3/blob/master/sub.hs#L66
<https://github.com/PierreR/pipes-zmq3/blob/master/sub.hs#L66>
Do I replace (input >-> P.take 10) with zoom (splitAt 10) drawAll
? Then how do I use the parser with Foldl ?
As a note, it seems to me that I don't need to check for stream
termination with zeromq because I always get one message or
nothing at all. The haskell zeromq lib takes care of dealing with
error conditions already.
Is that right ?
Thanks for your help,
Cheers
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