Sebastian Fischer wrote:
Holger Siegel wrote:
orElse :: CMaybe a a -> CMaybe a a -> CMaybe r a CMaybe ca `orElse` CMaybe cb = CMaybe (\k -> (ca return `mplus` cb return) >>= k)
I still don't understand why it is impossible to provide `orElse` with the original type. I will think more about the reason you gave.
The reason is that you have chosen the "wrong" type for your continuation monad; it should be newtype CMaybe a = CMaybe (forall r. (a -> Maybe r) -> Maybe r) Personally, I recommend to stop thinking about continuations altogether and instead use the approach I've outlined in "The Operational Monad Tutorial" http://apfelmus.nfshost.com/articles/operational-monad.html to define and think about monads. In particular, performing the refunctionalization I mentioned in the subsection "Connection with the Continuation Monad" shows that the "right" type should indeed contain a forall r . Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com