Abstract

Prototype-based languages are currently proposed as a substitute to class-based languages for a higher flexibility in manipulating objects. These languages are all based on a similar set of basic principles: object-centered representation, dynamic addition (deletion) of slots, cloning and message delegation. But they all differ in the precise interpretation of these principles and nobody has yet considered the semantic issues raised by their combination. In this paper, we propose a new taxonomy of prototypebased languages, enhancing the Treaty of Orlando by now discussing issues associated with the different semantics of the identified prototype-based languages. From this taxonomy, we extract a constructive proposal for the design of a new prototype-based language. This proposal is the chief result of this paper; it suggests one set of primitives which is regarded as the best to provide a clean, useful and coherent prototype-based computational model. We finally describe an implementation of most interesting language alternatives in the form of a Smalltalk-80 platform. This platform establishes an operational semantics for the basic primitives and -- more interesting -- validates our previous taxonomy by implementing it as a class hierarchy. Obviously, this platform has been used to relate in the same formalism the semantics of different languages with each others. For instance, the programming models of existing languages, such as Self, ObjectLisp and Actra's examplars, are faithfully derived as subclasses in this hierarchy.

Citations