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

Ertugrul, thanks for information. I've found several decisions for my real problem (using enumHandle and some more special decision). But I'll be have in mind about monad-control. 2011/4/3 Ertugrul Soeylemez

Bas van Dijk wrote:

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

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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/

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