Programming Language Design, Essays (university) of System Programming

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PROGRAMMING LANGUAGE

DESIGN CONCEPTS

PROGRAMMING LANGUAGE

DESIGN CONCEPTS

David A. Watt, University of Glasgow

with contributions by

William Findlay, University of Glasgow

Copyright  2004 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England Telephone (+44) 1243 779777

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Library of Congress Cataloging-in-Publication Data

Watt, David A. (David Anthony) Programming language design concepts / David A. Watt ; with contributions by William Findlay. p. cm. Includes bibliographical references and index. ISBN 0-470-85320-4 (pbk. : alk. paper)

1. Programming languages (Electronic computers) I. Findlay, William, 1947- II. Title. QA76.7 .W388 2004 005.13 – dc 2003026236

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 0-470-85320-

Typeset in 10/12pt TimesTen by Laserwords Private Limited, Chennai, India Printed and bound in Great Britain by Biddles Ltd, King’s Lynn This book is printed on acid-free paper responsibly manufactured from sustainable forestry in which at least two trees are planted for each one used for paper production.

Contents

Preface

The first programming language I ever learned was A LGOL60. This language was notable for its elegance and its regularity; for all its imperfections, it stood head and shoulders above its contemporaries. My interest in languages was awakened, and I began to perceive the benefits of simplicity and consistency in language design. Since then I have learned and programmed in about a dozen other languages, and I have struck a nodding acquaintance with many more. Like many pro- grammers, I have found that certain languages make programming distasteful, a drudgery; others make programming enjoyable, even esthetically pleasing. A good language, like a good mathematical notation, helps us to formulate and communi- cate ideas clearly. My personal favorites have been PASCAL, A DA , ML, and J AVA. Each of these languages has sharpened my understanding of what programming is (or should be) all about. P ASCAL taught me structured programming and data types. A DA taught me data abstraction, exception handling, and large-scale pro- gramming. ML taught me functional programming and parametric polymorphism. J AVA taught me object-oriented programming and inclusion polymorphism. I had previously met all of these concepts, and understood them in principle, but I did not truly understand them until I had the opportunity to program in languages that exposed them clearly.

Contents

This book consists of five parts. Chapter 1 introduces the book with an overview of programming linguistics (the study of programming languages) and a brief history of programming and scripting languages. Chapters 2–5 explain the basic concepts that underlie almost all programming languages: values and types, variables and storage, bindings and scope, procedures and parameters. The emphasis in these chapters is on identifying the basic concepts and studying them individually. These basic concepts are found in almost all languages. Chapters 6–10 continue this theme by examining some more advanced con- cepts: data abstraction (packages, abstract types, and classes), generic abstraction (or templates), type systems (inclusion polymorphism, parametric polymor- phism, overloading, and type conversions), sequencers (including exceptions), and concurrency (primitives, conditional critical regions, monitors, and rendezvous). These more advanced concepts are found in the more modern languages. Chapters 11–16 survey the most important programming paradigms, compar- ing and contrasting the long-established paradigm of imperative programming with the increasingly important paradigms of object-oriented and concurrent pro- gramming, the more specialized paradigms of functional and logic programming, and the paradigm of scripting. These different paradigms are based on different

xv

xvi Preface

selections of key concepts, and give rise to sharply contrasting styles of language and of programming. Each chapter identifies the key concepts of the subject paradigm, and presents an overview of one or more major languages, showing how concepts were selected and combined when the language was designed. Several designs and implementations of a simple spellchecker are presented to illustrate the pragmatics of programming in all of the major languages. Chapters 17 and 18 conclude the book by looking at two issues: how to select a suitable language for a software development project, and how to design a new language. The book need not be read sequentially. Chapters 1–5 should certainly be read first, but the remaining chapters could be read in many different orders. Chapters 11–15 are largely self-contained; my recommendation is to read at least some of them after Chapters 1–5, in order to gain some insight into how major languages have been designed. Figure P.1 summarizes the dependencies between the chapters.

Examples and case studies

The concepts studied in Chapters 2–10 are freely illustrated by examples. These examples are drawn primarily from C, C++, JAVA , and A DA. I have chosen these languages because they are well known, they contrast well, and even their flaws are instructive!

1 Introduction

2 Values and Types

4 Bindings and Scope

5 Procedural Abstraction

6 Data Abstraction

7 Generic Abstraction

11 Imperative Programming

12 OO Programming

15 Logic Programming

17 Language Selection

18 Language Design

3 Variables and Storage

8 Type Systems

14 Functional Programming

9 Control Flow

13 Concurrent Programming

16 Scripting

10 Concurrency

Figure P.1 Dependencies between chapters of this book.

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student will need to follow up with more advanced studies. The book has an extensive bibliography, and each chapter closes with suggestions for further reading on the topics covered by the chapter.

Acknowledgments

Bob Tennent’s classic book Programming Language Principles has profoundly influenced the way I have organized this book. Many books on programming languages have tended to be syntax-oriented , examining several popular languages feature by feature, without offering much insight into the underlying concepts or how future languages might be designed. Some books are implementation- oriented , attempting to explain concepts by showing how they are implemented on computers. By contrast, Tennent’s book is semantics-oriented , first identifying and explaining powerful and general semantic concepts, and only then analyzing particular languages in terms of these concepts. In this book I have adopted Ten- nent’s semantics-oriented approach, but placing far more emphasis on concepts that have become more prominent in the intervening two decades. I have also been strongly influenced, in many different ways, by the work of Malcolm Atkinson, Peter Buneman, Luca Cardelli, Frank DeRemer, Edsger Dijkstra, Tony Hoare, Jean Ichbiah, John Hughes, Mehdi Jazayeri, Bill Joy, Robin Milner, Peter Mosses, Simon Peyton Jones, Phil Wadler, and Niklaus Wirth. I wish to thank Bill Findlay for the two chapters (Chapters 10 and 13) he has contributed to this book. His expertise on concurrent programming has made this book broader in scope than I could have made it myself. His numerous suggestions for my own chapters have been challenging and insightful. Last but not least, I would like to thank the Wiley reviewers for their constructive criticisms, and to acknowledge the assistance of the Wiley editorial staff led by Gaynor Redvers-Mutton.

David A. Watt Brisbane March 2004

PART I

INTRODUCTION

Part I introduces the book with an overview of programming linguistics and a brief history of programming and scripting languages.