A novel programming language construct, restrictions, provides a mechanism to document abstract invariants of program variables and also may simplify program correctness proofs of the use of components. Examples illustrating the use and utility of restrictions are presented.

In a distributed system where many processors are connected by a network and communicate using message passing, many users can be allowed to access the same facilities. A public utility is usually an expensive or limited resource whose use has to be regulated. A guardian is an abstraction that can be used to regulate the use of resources by scheduling their access, providing protection, and imp...

Patternmatching is a programming language construct that is common in functional programming but somewhat less popular in object-oriented languages. The present paper gives an overview of issues that arise when adding pattern matching to an object-oriented language like Java.

The repertory grid test, based on personal construct psychology, was used to evaluate the effectiveness of Project P.A.T.H.S. (Positive Adolescent Training through Holistic Social Programmes) in Hong Kong. One hundred and four program participants (n = 104) were randomly invited to complete a repertory grid based on personal construct theory in order to provide both quantitative and qualitative...

Intensional type analysis is a language construct for run-time type analysis. In this paper we encode its static and dynamic semantics in a meta-logical framework. This deepens our understanding of the language and mechanizes the proofs of its properties. We make a special effort to obtain an elegant encoding that is faithful to the original presentation on

Any PDE system can be effectively analyzed through consideration of its tree of nonlocally related systems. If a given PDE system has n local conservation laws, then each conservation law yields potential equations and a corresponding nonlocally related potential system. Moreover, from these n conservation laws, one can directly construct 2 − 1 independent nonlocally related systems by consider...

This paper describes the design of a protocol stack implemented in Standard ML. Standard ML's signatures are a language construct which can be used to specify or constrain the interface of a module. The design includes both a generic signature which generalizes all the protocol modules, and individual signatures speci c to each protocol module. The speci c signatures all inherit from the generi...

We propose a novel language construct called communicating transactions, obtained by dropping the isolation requirement from classical transactions, which can be used to model automatic error recovery in distributed systems. We extend CCS with this construct and give a simple semantics for the extended calculus, called TransCCS. We develop a behavioural theory which is sound and complete with r...

We show how the PEPA performance modelling language could be extended with a feature construct which can be used to describe modifications to PEPA models. We provide this construct with an operational description which conservatively extends the operational semantics of the PEPA language. We then show how the feature construct can be applied in a small case study.