A Core Calculus of Classes and Mixins

We develop an imperative calculus that provides a formal model for both single and mixin inheritance. By introducing classes and mixins as the basic object-oriented constructs in a λ-calculus with records and references, we obtain a system with an intuitive operational semantics. New classes are produced by applying mixins to superclasses. Objects are represented by records and produced by instantiating classes. The type system for objects uses only functional, record, and reference types, and there is a clean separation between subtyping and inheritance.