Metric Semantics and Full Abstractness for Action Refinement and Probabilistic Choice

This paper provides a case-study in the field of metric semantics for probabilistic programming. Both an operational and a denotational semantics are presented for an abstract process language L_pr, which features action refinement and probabilistic choice. The two models are constructed in the setting of complete ultrametric spaces, here based on probability measures of compact support over sequences of actions. It is shown that the standard toolkit for metric semantics works well in the probabilistic context of L_pr, e.g. in establishing the correctness of the denotational semantics with respect to the operational one. In addition, it is shown how the method of proving full abstraction --as proposed recently by the authors for a nondeterministic language with action refinement-- can be adapted to deal with the probabilistic language L_pr as well

Modular Composition of Language Features through Extensions of Semantic Language Models

Today, programming or specification languages are often extended in order to customize them for a particular application domain or to refine the language definition. The extension of a semantic model is often at the centre of such an extension. We will present a framework for linking basic and extended models. The example which we are going to use is the RSL concurrency model. The RAISE specification language RSL is a formal wide-spectrum specification language which integrates different features, such as state-basedness, concurrency and modules. The concurrency features of RSL are based on a refinement of a classical denotational model for process algebras. A modification was necessary to integrate state-based features into the basic model in order to meet requirements in the design of RSL. We will investigate this integration, formalising the relationship between the basic model and the adapted version in a rigorous way. The result will be a modular composition of the basic process model and new language features, such as state-based features or input/output. We will show general mechanisms for integration of new features into a language by extending language models in a structured, modular way. In particular, we will concentrate on the preservation of properties of the basic model in these extensions

Stepwise refinement of heap-manipulating code in Chalice

Stepwise refinement is a well-studied technique for developing a program from an abstract description to a concrete implementation. This paper describes a system with automated tool support for refinement, powered by a state-of-the-art verification engine that uses an SMT solver. Unlike previous refinement systems, users of the presented system interact only via declarations in the programming language. Another aspect of the system is that it accounts for dynamically allocated objects in the heap, so that data representations in an abstract program can be refined into ones that use more objects. Finally, the system uses a language with familiar imperative features, including sequential composition, loops, and recursive calls, offers a syntax with skeletons for describing program changes between refinements, and provides a mechanism for supplying witnesses when refining non-deterministic programs

Exception Handling in C∀

The C∀ (Cforall) programming language is an evolutionary refinement of the C programming language, adding modern programming features without changing the programming paradigms of C. One of these modern programming features is more powerful error handling through the addition of an exception handling mechanism (EHM). This thesis covers the design and implementation of the C∀ EHM, along with a review of the other required C∀ features. The EHM includes common features of termination exception handling, which abandons and recovers from an operation, and similar support for resumption exception handling, which repairs and continues with an operation. The design of both has been adapted to utilize other tools C∀ provides, as well as fit with the assertion based interfaces of the language. The EHM has been implemented into the C∀ compiler and run-time environment. Although it has not yet been optimized, performance testing has shown it has comparable performance to other EHMs, which is sufficient for use in current C∀ programs

rCOS: A refinement calculus for object systems

This article presents a mathematical characterization of object-oriented concepts by defining an observation-oriented semantics for a relational objectoriented language with a rich variety of features including subtypes, visibility, inheritance, type casting, dynamic binding and polymorphism. The language is expressive enough for the specification of object-oriented designs and programs. We also propose a calculus based on this model to support both structural and behavioral refinement of object-oriented designs. We take the approach of the development of the design calculus based on the standard predicate logic in Hoare and He’s Unifying Theories of Programming (UTP). We also consider object reference in terms of object identity as values and mutually dependent methods