Design of a Concurrent and Distributed Language

This paper presents a new dialect of Scheme aimed towards con-currency and distribution. It ooers a few primitives, including rst-class continuations , with very simple semantics. Numerous examples are given showing how to program the classical concurrent control operators such as future, pcall and either. The implementation is sketched and presented along the lines of a metacircular interpreter. This paper presents the idiom of Icsla 1 , a language belonging to the Lisp family and more precisely a descendant of Scheme. This dialect has been designed with respect to the following main objectives: { It should have a very simple and understandable semantics, with few but powerful and unrestrictively combinable concepts; { It should ooer concurrency, distribution and some other modern features such as sophisticated control features while not sacriicing the variety of styles traditionally ooered by Lisp. These goals are rather general and deserve further comment. Following Scheme, the semantics must be kept small and clean; this in turn favors correct implementation , precise documentation and eases learning or teaching. The concepts must be understandable and simple, i.e. providing only one functionality since composition is already ooered at various levels by procedures, macros or modules. Existing concurrent features, proved useful in other languages, must be programmable|this demonstrates the power of our concepts as well as providing implementations that can be taught. Having no current user community to protect, some concepts have been freely revised, such as continuations, objects and equality. Currently the idiom lacks an abundance of features, since any feature that can be delivered by a library has been postponed. Finally we view our resulting idiom as a proto-language on top of which other languages can be built such as Scheme, EuLisp or CLOS. 1 Icsla (standing for interpretation, compilation and semantics of applicative languages) is the name of a joint project between Ecole Polytechnique and INRIA-Rocquencourt, hence the name of the designed language.