[Haskell-cafe] using IO monad in Iteratee

[Dmitry Olshansky]

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 <es at ertes.de>

> Bas van Dijk <v.dijk.bas at gmail.com> wrote:
>
> > On 1 April 2011 21:59, Dmitry Olshansky <olshanskydr at gmail.com> 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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