Instead of returning a `Producer` from your `Parser`, just consume the
parsed stream directly using `toParser` or `toParser_` from `Pipes.Parse`:
toParser :: Monad m => Consumer (Maybe a) m r -> Parser a m r
toParser_ :: Monad m => Consumer a m X -> Parser a m ()
For your code example specifically, you would probably want:
zoom (Pipes.Parse.span (/= "end")) (toParser_ Pipes.Prelude.print)
On 7/30/14, 1:26 PM, David McBride wrote:
In a larger program I have to parse events, and one of the events has
a start and end delimiter and then an unknown number of events in
between. Sounds like a job for pipes-parse. Here's some stripped
down code to show what I intended.
{-# LANGUAGE OverloadedStrings, LambdaCase #-}
import Pipes
import Pipes.Parse
import Pipes.Prelude
import Data.Text
import Control.Monad.State.Strict
import Control.Lens
getnums :: (Functor m, Monad m) => Parser Text m (Producer Text m ())
getnums = do
draw >>= \case
(Just "start") -> do
nums <- zoom (Pipes.Parse.span (/= "end")) $ do
undefined :: Parser Text m (Producer Text m ())
void skip
return nums
_ -> undefined
testgetnums :: IO ()
testgetnums = do
(p,rest) <- runStateT getnums $ Pipes.each
["start","1","2","3","4","end","morestuff"]
runEffect $ p >-> Pipes.Prelude.print
-- expected to print out roughly -> 1 2 3 4, with a rest producer
that has morestuff in it.
My goal is to end up with a producer that produces the numbers,
without the start or end events. I could just use drawAll and put its
result into Pipes.each, but it seems like I should be able to use zoom
(span (/= "end")) to get a parser that just has the numbers in it, and
then somehow turn that into a producer that I can return.
Am I even taking the right approach to this? Or should I be turning
to pipes group somehow? I tried that and felt like I didn't even get
close to a solution.
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