What are uses of polymorphic kinds?

Question

Polymorphic kinds are an extension to Haskell\'s type system, supported by UHC, allowing

data A x y = A (y x)

to be typed (kinded?) as a

Answer 1

They are useful for defining functions that operate over data constructors with arbitrary arity, of course!

A concrete example could be a function that, given a data constructor with arbitrary arity, returns a new data constructor that wraps the given constructor in Some().