Fundamental Concepts and Formal Semantics of Programming Languages

2003 Copies may be made for personal use only Preface These lecture notes are about the conceptual analysis and formal semantic description of programming languages. They explain how to analyse programming constructs in terms of fundamental concepts, and how to formulate precise descriptions of their intended interpretation using the structural approach to operational semantics. The practical applicability of this approach to real programming languages is illustrated by describing constructs taken from Standard ML and Concurrent ML. A novel feature of this course is the use of a recently-developed variant of the structural operational semantics framework, called MSOS. This variant has the advantage of providing an exceptionally high degree of modularity: definitive descriptions of individual language constructs can be formulated independently, and remain unchanged when further constructs are added to the described language. Conventional structural operational semantic descriptions do not enjoy this property , and sometimes require extensive reformulation, for instance when adding side-effects or communicating processes to a purely functional language. A transcription of semantic descriptions into Prolog allows programs in the described language to be run according to their semantics. This helps to see how the given rules work, and to validate new rules. The notes also consider (albeit very briefly) alternative approaches to formal semantics, including action semantics, axiomatic semantics, denotational semantics , and other forms of operational semantics. The aim here is merely to provide students with a general awareness of the main approaches to formal semantics; references to the literature are provided for those who wish to continue with more advanced studies in this area. About these lecture notes: The material in these notes is intended to be read in the order in which it appears. It is strongly recommended to try most of the exercises listed at the end of each chapter: this checks that the presented material has been properly grasped, and provides further illustration of various points. A reference to an exercise in the margin indicates that the material required for the exercise has now been covered. i PREFACE ii All the main points in these notes are displayed like this.. . Each point is followed by further explanations and/or illustrations. The display of the main points should help to keep an overview of the main line during a first reading (when the intervening material may even be skipped, if desired) as well as facilitating revision. About the course based on these notes: …