Re: [Haskell-beginners] Constrained polymorphic functions as natural transformations

On Fri, Dec 13, 2013 at 10:25 PM, Matt R wrote:

Interesting to discover that not all polymorphic functions are natural transformations. "fix" seems rather exotic -- are there any less unusual examples?

None of the church numerals of type (a -> a) -> (a -> a) are natural transformations either: zero _ = id one f = f two f = f . f three f = f . f . f etc. -- Kim-Ee