Hi,
I am learning pipes and trying to figure out the following example:
I have a stateful consumer, let's say a counter:
counter :: (Show a) => Consumer a (StateT Integer IO) ()
counter = do
x <- await
lift $ S.modify (+1)
liftIO $ print $ show x
counter
But how do I get the final state from it?
The following code wouldn't work because the producer ("each") has value
type of unit, and the consumer seems to be required to return the same
value type:
--this doesn't compile
runEffect $ each [1,2,3,4,5,6] >-> PL.execState 0 counter
Am I approaching the problem incorrectly?
I'd like to have a pipeline that runs "normally", ideally even with
"normal" stateless consumers, but also accumulates some data that is not
needed for the pipeline itself, but is useful when it is finished.
Something as simple as:
each [1,2,3,4,5,6] >-> .... >-> P.print
and that would return a count of elements handled by the pipeline when it
has finished.
Maybe I should be wrapping the whole producer into StateT, something like
StateT (Producer a m r) m r? Then how to compose the pipeline with this
type?
Or what would be the way to solve this kind of problem?
Cheers,
Alexey.
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