Interface Types for Haskell

Abstract. Interface types are a useful concept in object-oriented pro-gramming languages like Java or C#. A clean programming style advo-cates relying on interfaces without revealing their implementation. Haskell’s type classes provide a closely related facility for stating an in-terface separately from its implementation. However, there are situations in which no simple mechanism exists to hide the identity of the imple-mentation type of a type class. This work provides such a mechanism through the integration of lightweight interface types into Haskell. The extension is non-intrusive as no additional syntax is needed and no existing programs are affected. The implementation extends the treat-ment of higher-rank polymorphism in production Haskell compilers.