[Haskell-beginners] Constrained polymorphic functions as natural transformations

[Kim-Ee Yeoh]

On Fri, Dec 13, 2013 at 10:25 PM, Matt R <habari.zerglings at gmail.com> 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
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