Abstract

The type systems of functional languages such as Haskell have recently become more powerful and expressive. They not only allow programmers to write code that works on values of any type (genericity), they also allow programmers to require that a particular type belongs to a given type class (constrained genericity). Such code may use any of the methods listed in the interface of the type class, since every type that is a member of the type class must implement those methods. This capability makes it significantly easier to express solutions to many common problems, and promotes code reuse. Incorporating type classes in a logic programming language provides some new challenges. In this paper, we explain how we have extended Mercury's type system to include support for type classes. We give a formal semantics for this extension to our type system, adapting the typing rules used in functional languages to the differing demands of logic programming languages. We show that type classes in...

Citations