If there was no Conduit.mapM

conduit.hs

getPersonStream :: ConduitT () PeopleRequest ServerErrorIO ()
                -> ConduitT PeopleResponse Void ServerErrorIO ()
                -> ServerErrorIO ()
getPersonStream source sink = runConduit $ source .| reStream .| sink
  where
    reStream = do
      req <- await
      case req of
        Nothing -> return ()
        Just r -> do
          liftIO $ threadDelay (2 * 1000 * 1000)
          yield $ evolvePerson r
          reStream