o...@okmij.org writes:
> class Functor' f a b where
> fmap' :: (a -> b) -> f a -> f b
I was about to ask why you mentioned b in the type signature as well, as
I thought just having "(Functor' f b)" as a constraint in the type
signature of fmap' would be sufficient, but when I went to check I
But that's not really a solution, since it doesn't make a Functor
instance for Set; it makes a Functor' instance for Set.
If you are willing to not be upwards compatible then, yes, there are solutions.
I think the best bet for an upwards compatible solutions is the
associated constraints,
www.cs.k
Lennart Augustsson wrote:
> Try to make Set an instance of Functor and you'll see why it isn't.
> It's very annoying.
And yet the very simple, and old solution works.
http://okmij.org/ftp/Haskell/types.html#restricted-datatypes
We just properly generalize Functor, so that all old funct
