Subtypes: Scope, Event, Match.
Contravariant Endo Functor from Arrow into Arrow (1/2 argument):
Contravariant Endo Functor from Arrow into Arrow (1/2 argument) factoring through Void:
Covariant Endo Functor from Arrow into Arrow (2/2 argument):
Covariant Endo Functor from Arrow into Arrow (2/2 argument) factoring through Unit: