Abstract:

This paper elucidates the essence of Object-Oriented Programming (OOP), using a constructive approach: we identify a minimal basis of concepts with which to synthesize existing and potential object systems. We reduce them to constructions atop the pure untyped lambda calculus, thereby obtaining both denotational semantics and effective implementation. We start from the simplest recognizable model of prototype-based OOP, so simple it arguably does not even have “objects” as such. We build further models of increasing sophistication, reproducing a growing subset of features found in past object systems, including original combinations. We also examine how our approach can deal with issues like typing, modularity, classes, mutation. We use Scheme to illustrate our approach.