The newly released coroutine-enumerator package can be used as a bridge between the enumerator and monad-coroutine packages. It provides two-way conversion functions between an Iteratee and an Await-suspending coroutine, and also between an Enumerator and a Yield-suspending coroutine. As a little example, the following program combines the http-enumerator, monad-coroutine, and SCC packages using the coroutine-enumerator package to print out all lines from the Hackage database containing substring "enumerator":
import Control.Exception.Base (SomeException) import Control.Monad.Trans.Class (lift)
import Data.ByteString (ByteString) import Data.Text.Encoding (decodeUtf8)
import Network.HTTP.Enumerator
import Control.Monad.Coroutine import Control.Monad.Coroutine.SuspensionFunctors import Control.Monad.Coroutine.Nested import Control.Monad.Coroutine.Enumerator
import Control.Concurrent.SCC.Sequential
main = httpRedirect (\_ _-> coroutineIteratee consumer) =<< parseUrl address
address = "http://hackage.haskell.org/packages/archive/pkg-list.html"
consumer :: Coroutine (Await [ByteString]) IO (Either SomeException ((), [ByteString])) consumer = pipe translator (consume worker) >> return (Right ((), []))
translator :: Functor f => Sink IO (EitherFunctor (Await [a]) f) a -> Coroutine (EitherFunctor (Await [a]) f) IO () translator sink = do chunks <- liftParent await if null chunks then lift (putStrLn "END") else putList chunks sink >> translator sink
worker :: Consumer IO ByteString () worker = toChars >-> foreach (line `having` substring "enumerator") (append (fromList "\n") >-> toStdOut) suppress
toChars :: Monad m => Transducer m ByteString Char toChars = oneToOneTransducer decodeUtf8 >-> coerce
Alternatively, the worker coroutine can parse the XML database and print out all elements whose any attribute value contains the substring "enumerator":
worker = toChars >-> parseXMLTokens >-> foreach (xmlElementHavingTagWith (xmlAttributeValue `having` substring "enumerator") `nestedIn` xmlElementContent) (coerce >-> toStdOut) suppress