62 Book Reviews

this might prove inadequate, more formal definitions have been included. The notation is not rigorous and the text is not intended as a replacement for the formal definitions of the languages to be found in the various defining documents.

The approach throughout is distinctly from the point of view of the user of programming languages, that is, someone who wants to write programs, and not from the point of view of the designer or the implementor.

Applied APL Programming. WILBUR R. LEPAGE (Prentice-Hall, Englewood Cliffs, N J) In general terms, this book deals with the use of computers to solve practocal problems, using APL language

as a vehicle. Various programming languages succeed in different ways and to different degrees in bridging the gap between the way a person conceives a solution and the instructions a computer can "comprehend." APL is a programming language for which the gap is small.

In the choice of illustrative examples, an attempt has been made to make them simple enough so as to not detract from the programming concepts being illustrated, but sophisticated enough to illustrate nontrivial features of the language. Examples are chosen from a wide range of applications so that the reader will perceive the pertinence of computing to many fields of activity.

The mathematical level required for most of the book is algebra (the transcendental functions are exceptions). Although the mathematical prerequisite is not high, the subject is treated in depth and is graduated in difficulty in the expectation that the reader's level of sophistication will rise during progress through the book.

The APL notation has certain features of "'style" that tend to provide simpler conceptualizations than would otherwise be evident. To learn APL well is to incorporate these features of style into one's mode of thinking. Therefore, style considerations are stressed, including APL versions of the concepts of structured programming.

Chapter 1 gives an overview of computing, emphasizing the importance of developing an algorithmic approach, and is included for the reader who is interested in a philosophical appraisal of what computing is about.

Chapters 2 through 5 contain the basic information about APL and its application to practical problems. Because these chapters must be learned thoroughly, a series of questions is included, providing the reader with a mechanism for continual self appraisal. In Chaps. 2 through 4 these questions are on the margins of the pages of text; in Chap. 5 they are grouped at the end of the chapter, arranged according to related section numbers.

Chapter 6 deserves special mention because of its unique nature. It presents general treatments of many of the features of APL which are presented in simplified form in the earlier chapters. The subtle points dealt with in this chapter are essential in the sophisticated use of APL.

Chapters 7 and 8 deal with further refinements, particularly the use of shared variables, and how the concepts of structured programming can be used in APL. These two chapters contain material that a mature user of APL would be expected to know, but to some extent they may be considered optional in an introductory course of study.

Slructured Programming and Problem-Solving with PL/I. RICHARD B, KIEBURTZ (Prentice-Hall, Englewood Cliffs, N J)

This book is an introduction to problem solving by computational methods. If it helps you to learn how to specify the requirements for a solution, how to formulate, one step at a time. a procedure to follow in generating a solution, and how to describe that procedure so that it may be understood by others, then it will have succeeded in its purpose.

One of the principal ways in which this book differs from most introductory computer texts is that it emphasizes a more disciplined approach to the design of computational procedures.

In this book, the programming language PL/I is used as a vehicle for the description of computational procedures. In order to render some computations more readily understandable, the programming language will be augmented with comments in English.

Structured Programming in A PL DENNIS P. GELLER and DANIEL P. FREEDMAN, (Winthrop, Cambridge, MA) This is an introductory book on programming and on the computer language, APL. It is suitable for

beginning programming students from junior college to graduate school, for in-house education in industry, or for self-study by experienced programmers who wish to learn APL. This book embodies an approach which is quite different from the other books now available. Our aim is to bring the student very early to the point of writing working programs: further details on our approach and how to use the book most effectively are presented in the following paragraphs.

The book falls naturally into three sections of three chapters each. The first section deals with the basic concepts of programming and of APL: we introduce structure charts for describing algorithms, and then examine the data structures and operators of APL. The chapters in the second section teach the student to write programs from algorithms which have been expressed as structure charts. The third section deals with the design and development of programs, and of systems of programs. Also, sprinkled throughout the book, are Interludes which discuss important mechanical aspects of APL: signing on, creating and saving workspaces, using APL as an aid to debugging.

A Teacher's Manual is available as a companion to the book, containing suggestions for teaching from the text, and for additional material which might be presented. The Manual also contains a large number of classroom tested "visuals"--these can be detached and copied on transparencies for overhead projection.

Chapter 1 introduces structure charts as a vehicle for expressing algorithms. Later, when students begin programming in APL they first learn to express their structure charts as APL programs. Chapters 2 and 3 discuss the data structures and operators of APL.

Chapter 3 discusses a number of operators, but also presents general principles which provide a framework for learning about the others. This learning is encouraged by the exercises, in which students are led to find out about operators not covered in the text.