Modular Generic Programming with Extensible Superclasses

"Generics for the Masses" (GM) and "Scrap your Boilerplate" (SYB) are generic programming approaches based on some inenious applications of Haskell type classes. To achieve modularity, the GM and SYB approach have been extended by using some experimental language extensions such as abstraction over type classes and recursive instances. Hence, the type class encodings behind the GM and SYB approach become less practical and harder to understand.We show that none of these type class features are necessary if we use the single feature of extensible superclasses, the complement of subclass extension. We formalize type classes with extensible superclasses as the combination of a previously introduced type-passing translation scheme and a general type class framework. Our results shed some new light on the use of type classes to support generic programming.