As of March 2020, School of Haskell has been switched to read-only mode. What is lens?lens is a package which provides the type synonym Lens which is one of a few implementations of the concept of lenses, or functional references. lens also provides a number of generalizations of lenses including Prisms, Traversals, Isos, and Folds. Why do I care?Lenses and their cousins are a way of declaring how