Peter J. L. Wallis

Viewpoint specification and Z

Abstract In the paper we discuss the use of viewpoint specifications, a technique which concentrates on making large specifications more understandable. Rather than specifying the whole system at once, a system is described using several self-contained partial specifications, which may then be amalgamated to give a description of the complete system. Amalgamation is taken to be a composite process in which the data and operations of the constituent viewpoints are separately considered. The approach is illustrated in terms of Z specifications.

Conversion of FORTRAN to Ada using an intermediate tree representation

On decrit un convertisseur de FORTRAN a ADA qui utilise une representation arboresque intermediaire standard du programme qui doit etre converti. Le systeme existant et les conversions employees a quelques instructions FORTRAN selectionnees sont decrits en detail

External Representations of Objects of User-Defined Type

The portable programming language (PPL) is one of a number of recently designed programming languages that enable the user to define new types by giving their representations and operations in terms of those of previously available types. Such provisions for the construction of objects of user-defined type have been discussed elsewhere; this work concerns the related problem of the external representations of such objects, both on input-output media and as written constants within the program text. We introduce an enhancement to the PPL design allowing specification of the external representations of objects of user-defined type. This extension to the PPL design means that objects of user-defined type can be read, written, and used as constants exactly as if their representations had been selected by the writer of the PPL compiler. The implementation and use of the added facilities are also discussed.

The design and implementation of a high-level language converter

There is now a good understanding of problems encountered in the design, implementation and use of a high‐level language converter. These general issues are illustrated in terms of an account of the design and implementation of one particular converter, which converts programs from Pascal‐SC (a Pascal dialect) to Ada. A specific aim of the presentation is to provide guidance for those contemplating future language conversion projects.

Refinement methods and refinement calculi

A number of modern approaches to refinement are discussed and compared, and their broad classification into refinement methods and refinement calculi is explained. The refinement methods concerned are all based on the model-based specification languages VDM and Z, whereas the refinement calculi are all developments of the Dijkstra programming calculus. A generalised comparison of the refinement methods and the refinement calculi is also given.

Some primitives for the portable programming of array and vector processors

A high-level language for array and vector processors is analyzed by the methods of denotational semantics. The analysis leads to the identification of a set of primitives suitable for the portable programming of array and vector processors. Discussion of the primitives includes consideration of the efficiency with which they may be implemented on different machines, and their possible application to portable programming, the design of intermeiate languages, and the design of future array and vector processors.

The preparation of guidelines for portable programming in high-level languages

Programming even in a folly standardized high-level language requires great care if portable programs are to result. We review two recent attempts at producing guidelines for portable programming in high-level languages. Areas of particular difficulty, software aids to monitor compliance with projected guidelines, the prospects for enhanced portability of future languages and the form of published guidelines are separately discussed.

Planning for Portability

In this chapter we consider those issues affecting planning for portability that are separate from details of how the portable programs themselves are to be written. The subject is introduced by considering the functions of the donor and the installer of a piece of portable software. We then consider in some detail the kinds of documentation and testing appropriate for portable software.

The design of a portable programming language

SummaryWe consider the design of a strongly-typed language with userdefined types in which it is arranged that, given that a type is available, it is immaterial to the user whether it is a user-defined type or one of the “primitive types” with representations selected by the implementer. This scheme provides unprecedented freedom in choosing the primitive types; by making these machine-dependent we can ensure production of programs that are easily and efficiently portable between computers of different architectures. A general discussion of the implementers responsibilities in choosing primitive types appropriate to his machine is illustrated by considering implementation choices for translation of the language into BCPL. Finally we discuss the contribution of the language to the solution of the portability problem.

Requirements analysis for Ada compilers

A Guide to the Selection and Specification of Ada Compilers was recently produced by the Portability Working Group of Ada-Europe. Most of the points addressed are applicable criteria for evaluation of any language compiler.