@hackage constrained0.1

This package generalizes familiar Functor, Foldable and Traversable for the case when a functorial type of kind Type -> Type imposes certain constraints on what can be put in. E.g. Set can only deal with types that are an instance of Ord and therefore cannot be made an instance of Functor. But it can be made an instance of a constrained functor with a similar interface that this package provides.