A Modular SOS for ML Concurrency Primitives

Abstract

Modularity is an important pragmatic aspect of semantic
descriptions. In denotational semantics, the issue of modularity has
received much attention, and appropriate abstractions have been
introduced, so that definitions of semantic functions may be independent of
the details of how computations are modeled. In structural operational
semantics (SOS), however, this issue has largely been neglected, and
SOS descriptions of programming languages typically exhibit rather poor
modularity| - for instance, extending the described language may entail
a complete reformulation of the description of the original constructs.
A proposal has recently been made for a modular approach to SOS, called
MSOS. The basic definitions of the Modular SOS framework are recalled
here, but the reader is referred to other papers for a full introduction.
This paper focuses on illustrating the applicability of Modular SOS, by
using it to give a description of a sublanguage of Concurrent ML (CML);
the transition rules for the purely functional constructs do not have to be
reformulated at all when adding references and/or processes. The paper
concludes by comparing the MSOS description with previous operational
descriptions of similar languages.
The reader is assumed to be familiar with conventional SOS, with the
concepts of functional programming languages such as Standard ML, and
with fundamental notions of concurrency.