A natural transformation package.

A natural transformation transforms a container f a into another container g a. Natural transformations act as functor morphisms in category theory.

The naming of ~>, :~> and $$ were taken, with permission, from Edward Kmett's indexed package.

natural-transformation

A natural transformation transforms a container f a into another container g a. Natural transformations act as functor morphisms in category theory. Technically, f and g should be functors, but we allow any correctly-shaped structure.