Title: Department of Computer Science Seminar
Date: Friday, Nov. 24, 2000
Time: 11:00 am to 12:30 pm
Venue: Room N101, CSIT Building [108]
Speaker: Luigi Liquori, Ecole Nationale Supérieure des Mines de Nancy & LORIA
Description: "Prototype-based languages and a framework for object calculi"


                        Abstract


In this talk we investigate, in the context of functional
prototype-based languages, objects which might extend themselves upon
receiving a message. The possibility for an object of extending its
own ``self'', referred to by Cardelli, as a self-inflicted operation,
is novel in the context of typed object-based languages. We present a
sound type system for this calculus which guarantees that evaluating a
well-typed expression will never yield a message-not-found run-time
error.  We give several examples which illustrate the increased
expressive power of our system with respect to existing calculi of
objects. The new type system allows also for a flexible
width-subtyping, still permitting sound method override, and a limited
form of object extension. The resulting calculus appears to be a good
starting point for a rigorous mathematical analysis of class-based
languages.

Moreover, we give a general framework for the foundation of an
operational (small step) semantics of object-based languages with an
emphasis on functional and imperative issues. The framework allows
classifying very naturally many object-based calculi according to
their main implementation techniques of inheritance, namely delegation
and embedding, and their particular strategies.  This distinction
comes easily from a choice in the rules.  Our framework is founded on
two previous works: lambda-Obj+, a version of the Lambda Calculus of
Objects of Fischer, Honsell, and Mitchell, for the object aspects, and
lambda-sigma-a-w of Benaissa, Lescanne, and Rose, for the description
of the operational semantics and sharing.  The former is the
formalization of a small delegation-based language which contains both
lambda calculus and object primitives to create, update, and send
messages to objects, while the latter is designed to provide a generic
description of functional language implementations and is based on a
calculus of explicit substitution extended with addresses to deal with
memory management.


URL: http://cs.anu.edu.au/lib/seminars/seminars00/dept20001124b