Hello. IMHO there are 2 ways to define categories in Haskell: W0) the category of types and functions ("base.Data.Functor" and company belongs to it); W1) the class "base.Control.Category.Category". (Defining a category where the class of objects is a type seems impossible in Haskell.) But these ways are mingled in "base". E.g. "Control.Applicative" (W0) and "Control.Category" (W1) are neighbors. Oddly, "Data.Functor" (W0) is under "Data". I believe that the whole library "category-extras" belongs to W1. I suggest to split these ways under distinct names, e.g.: W0) Category.Function (@hom == (->)@); W1) Category.Hom ("hom" is an abstract type constructor). Maybe both should be under "Mathematics".