Connect-and-resume a conduit

upcaseUntil.hs

import Conduit
import Data.Char (toUpper)

upcaseUntil :: (Monad m) => Char -> ConduitT Char Void m String
upcaseUntil breaker = takeWhileC (/= breaker) .| mapC toUpper .| sinkList

resumeAfter :: (Monad m) => ConduitT () Char m () -> ConduitT Char Void m String -> ConduitT () Char m ()
resumeAfter source process = do
  (next, begin) <- lift $ source $$+ process
  yieldMany begin
  unsealConduitT next

main :: IO ()
main = do
  putStrLn $
    runConduitPure $
      yieldMany "foo:bar" `resumeAfter` upcaseUntil ':' .| sinkList