A universally quantified function, usually written as F ~> G,
for symmetry with A => B.
Can be used to encode first-class functor transformations in the
same way functions encode first-class concrete value morphisms;
for example, sequence from scalaz.Traverse and cosequence
from scalaz.Distributive give rise to ([a]T[A[a]]) ~> ([a]A[T[a]]), for varying A and T constraints.
- Companion
- object