Very interesting, thanks. I didn't feel your classes yet... Do you think that provide these instances for Iteratee is possible? 2011/4/2 Bas van Dijk

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.

Good luck,

Bas

[1] http://hackage.haskell.org/package/monad-control

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:

...

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/

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