[Haskell-cafe] Higher order functor package?

[Mario Blažević]

On 2017-07-07 12:48 AM, Clinton Mead wrote:
> Consider the illustrative code below:
> ...
>     class MyFunctor f where
>        myFmap :: (forall a. t a -> u a) -> f t -> f u
> ...
> 
> 
> Basically this is a sort of "higher order" functor, but I can't seem to 
> fit it into an ordinary functor.
> 
> But it seems like I'm reinventing the wheel, as my code is suspiciously 
> like `Functor` but only slightly different.
> 
> Has this sort of class already been created and if so what package is it in?

Yes, I have recently created rank2classes package:

    http://hackage.haskell.org/package/rank2classes

	Apart from the mirror-universe Functor class, the package exports the 
Applicative, Foldable, Traversable, Applicative, and Distributive 
classes, as well as some Template Hashell to derive some of their 
instances automatically.