Book review

Abstract

Object-Oriented Programming in Common LISP is a very useful introduction to the new Common LISP Object System (CLOS). CLOS is a new object oriented programming system that combines many of the best features found in previous systems. It provides a clean and consistent semantic model in an extensible framework that can be efficiently implemented on stock hardware. The CLOS standard was recently approved as part of ANSI Standard Common LISP by the ANSI X3J13 committee.The standardization of the various dialects of LISP into Common LISP had the effect of dramatically improving the quality of the LISP that most programmers had to work with. The inclusion of CLOS in Common LISP should have the same effect on object oriented programming. CLOS provides one more standardized tool available to LISP programmers. It is a tool that is particularly useful for the construction of medium to large programs that are written by multiple authors and are intended to last a long time. It is generally easier to understand and extend a well designed object oriented program than a conventional program.These considerations make learning CLOS an important goal for Common LISP programmers. Keene's book is intended as an introduction both to the art of object oriented programming in general and to the characteristics of CLOS. It does a good job addressing both of these goals. Its primary audience will be experienced LISP programmers, although some attempt is made to make the book accessible to non-LISP programmers. But to the latter group, the explanations of LISP are not thorough enough to make the book useful.The overall structure of the book is excellent. The first and second chapters describe some of the benefits of object oriented programming and how CLOS extends Common LISP. This serves as a motivation for LISP programmers to learn CLOS. The second chapter also gives an excellent intuitive description of the basic CLOS concepts of classes, instances, slots, inheritance, generic functions and methods. This description includes some pictures which clearly demonstrate the CLOS conceptual model.As the book progresses, it introduces more detail into the conceptual model and describes the functions that are used to implement those features. Each function is introduced in the context of writing a specific example. The book also anticipates reader questions by including references to later sections which fill in details that were suppressed for the purposes of explaining a particular function. Summaries of important points are set off from the surrounding text in tables and boxes that are easy to