On Jun 15, 2010, at 6:11 PM, Sebastian Fischer wrote:
orElse :: CMaybe a a -> CMaybe a a -> CMaybe r a
CMaybe ca `orElse` CMaybe cb = CMaybe (\k -> (ca return `mplus` cb
return) >>= k)
Good point.
But with this restricted type `orElse` is less useful. For example,
one cannot compute
fromCMaybe ((return False `orElse` return True) >>= guard)
because there, the arguments of `orElse` are of type `CMaybe () Bool`.
Silly me! It's not the type of the *arguments* which is `CMaybe ()
Bool` but the type of the *result* of `orElse`, which is perfectly
possible with your implementation!
The type may be general enough. Interesting twist!
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.
Sebastian
--
Underestimating the novelty of the future is a time-honored tradition.
(D.G.)
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
