Fifty years of Hoare's Logic

We present a history of Hoare's logic.Comment: 79 pages. To appear in Formal Aspects of Computin

Array operators using multiple dispatch: a design methodology for array implementations in dynamic languages

Arrays are such a rich and fundamental data type that they tend to be built into a language, either in the compiler or in a large low-level library. Defining this functionality at the user level instead provides greater flexibility for application domains not envisioned by the language designer. Only a few languages, such as C++ and Haskell, provide the necessary power to define $n$-dimensional arrays, but these systems rely on compile-time abstraction, sacrificing some flexibility. In contrast, dynamic languages make it straightforward for the user to define any behavior they might want, but at the possible expense of performance. As part of the Julia language project, we have developed an approach that yields a novel trade-off between flexibility and compile-time analysis. The core abstraction we use is multiple dispatch. We have come to believe that while multiple dispatch has not been especially popular in most kinds of programming, technical computing is its killer application. By expressing key functions such as array indexing using multi-method signatures, a surprising range of behaviors can be obtained, in a way that is both relatively easy to write and amenable to compiler analysis. The compact factoring of concerns provided by these methods makes it easier for user-defined types to behave consistently with types in the standard library.Comment: 6 pages, 2 figures, workshop paper for the ARRAY '14 workshop, June 11, 2014, Edinburgh, United Kingdo

The development of an incremental debugging system : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Computer Science at Massey University

Debugging is a major area of software development that has received little attention. This thesis starts by looking at work done in the area of bug prevention, bug detection, bug location and bug correction. A debugging system, BIAS, is proposed to help in detecting, locating and correcting bugs. Three major design goals are established. Firstly, the system should be simple and easy to understand as this will encourage use. Secondly, the system should be general so that it will be available to a large number of users. Finally, it should be incremental as this will save users' time. An incremental language, STILL, is designed to show how BIAS applies to structured languages. The construction of the system is shown. Each data structure, and how it is used, is described. BIAS uses an interpretive system and runs threaded code on a pseudo-machine. How the threads are interpreted and how they are set up is shown next. The use of BIAS is shown by following through an example session with the system. This consists of entering a program, editing it, and running it. As bugs show themselves, various debugging commands are used to locate the bugs. The program is then edited, and the corrections linked into the code so that it will run correctly. This cycle is repeated until no bugs remain, without at any time recompiling the whole program. It turns out that the best way of achieving the design goals is to extend an incremental compiler host to include debugging commands. This gives a clear emphasis to the power of incremental compilers

Development of an MSC language and compiler, volume 1

Higher order programming language and compiler for advanced computer software system to be used with manned space flights between 1972 and 198

Automating the teaching of artificial language using production systems

The work to be described here is an investigation into the means whereby the learning of programming languages may be made easier. The role of formal definitions of programming languages is studied and a system is described which utilises production systems as the basis for generating an environment in which students may test their understanding of programming languages. This system for automating the teaching of programming languages provides an experimental testbed for carrying out further investigations into programming behaviour

Research in mathematical theory of computation

Research progress in the following areas is reviewed: (1) new version of computer program LCF (logic for computable functions) including a facility to search for proofs automatically; (2) the description of the language PASCAL in terms of both LCF and in first order logic; (3) discussion of LISP semantics in LCF and attempt to prove the correctness of the London compilers in a formal way; (4) design of both special purpose and domain independent proving procedures specifically program correctness in mind; (5) design of languages for describing such proof procedures; and (6) the embedding of ideas in the first order checker

Local constraints in programming languages part I: syntax

AbstractThe method of local constraints attempts to describe context-free languages in an apparently context-sensitive form which helps to retain the intuitive insights about the grammatical structure. This form of description, while apparently context-sensitive is, in fact, context-free and allows a program derivation structure to be represented as a tree with additional constraints, thus allowing for the possibility of a correctness proof in the form of Knuthian semantics. These semantic aspects will be discussed in a sequel to this paper (Part II: Semantics). Several detailed examples are given to motivate the use of local constraints grammars including some examples from the syntax of ALGOL 60. A parsing algorithm has been described; its purpose is to show that the computation of local constraints is quite reasonable. Transformation rules for transferring a context-free grammar into a local constraints grammar have been described and some heuristic approaches for the inverse transformation have been presented