On object extension

Abstract

The last few years have seen the development of statically typed object based (also called prototype-based) programming languages. Two proposals, namely the Lambda Calculus of Objects of Fisher, Hon-sell, and Mitchell [15], and the Object Calculus of Abadi and Cardelli [2], have focused the attention of the scientific community on object calculi, as a foundation for the more traditional class-based calculi and as an original and safe style of programming. In this paper, we apply four type systems to the functional Lambda Calculus of Objects: (a) the Original type system [15]; (b) the Fisher's Ph.D type system [14]; (c) the Bruce's Matching-based type systems of Bono and Bugliesi [4], and (d) of Liquori [20]. We then compare these type systems with respect to the following points: – small-step versus big-step semantics; – implicit versus explicit polymorphism; – Curry style versus Church style; – static type checking versus run-time type checking; – object extension and/or binary methods versus object subsumption (short account).