Actegories

# Summary Bartosz Milewski explains actegories, a fundamental concept in programming optics (lenses, prisms, traversals), by first defining monoidal categories—categories equipped with an associative and unital tensor product functor. He then shows how to model monoidal categories in Haskell using bifunctors and constraints, with practical examples like cartesian products and the Either type. An actegory is subsequently introduced as a category that supports the action of a monoidal category, functioning like a "scaling" operation on objects.