Re: [Haskell-cafe] using IO monad in Iteratee

Bas van Dijk wrote:

On 1 April 2011 21:59, Dmitry Olshansky wrote:

...

Is it possible to change enumFile to using MonadIO class?

No because it uses the control operation Control.Exception.finally :: IO a -> IO b -> IO a internally. You can't lift control operations with liftIO :: MonadIO m => IO a -> m a.

However if you are able to define a MonadTransControl and MonadControlIO instance (from the monad-control package[1]) for Iteratee and use Control.Exception.Control.finally instead of the regular finally, you can use your MyMonad with the modified enumFile.

I don't think that's possible, because Iteratee is based on CPS. I think, so far nobody has come up with an instance definition for monad-peel or monad-control for CPS-based monads like ContT or Iteratee. However, it is easy to write an own handle enumerator, which uses monad-peel or monad-control exception handling to convert errors to iteratee exceptions. On the other hand, as has been noted, there is enumHandle, which does that by itself. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/