A typed lambda calculus of objects

Abstract

In this paper, we present an explicitly typed version of the Lambda Calculus of Objects of [7], which is a development of the object-calculi defined in [10, 2]. This calculus supports object extension in presence of object subsumption. Extension is the ability of modify the behavior of an object by adding new methods (and inheriting the existing ones). Object subsumption allows to use objects with a bigger interface in a context expecting another object with a smaller interface. This calculus has a sound and decidable type system, “width” subtyping, and it allows for first-class method bodies.