Plan of the Book

• Functions

  Since functions are the foundation of Lisp programs, the book begins with several chapters on functions.

  • Chapter 2 explains what Lisp functions are and the possibilities they offer.
  • Chapter 3 then discusses the advantages of functional programming, the dominant style in Lisp programs.
  • Chapter 4 shows how to use functions to extend Lisp.
  • Chapter 5 suggests the new kinds of abstractions we can define with functions that return other functions.
  • Chapter 6 shows how to use functions in place of traditional data structures.
• Macros

  The remainder of the book deals more with macros than functions. Macros receive more attention partly because there is more to say about them, and partly because they have not till now been adequately described in print.

  • Chapters 7–10

    form a complete tutorial on macro technique. By the end of it you will know most of what an experienced Lisp programmer knows about macros: how they work; how to define, test, and debug them; when to use macros and when not; the major types of macros; how to write programs which generate macro expansions; how macro style differs from Lisp style in general; and how to detect and cure each of the unique problems that afflict macros.

  • Chapters 11–18

    show some of the powerful abstrac- tions you can build with macros.

    • Chapter 11 shows how to write the classic macros—those which create context, or implement loops or conditionals.
    • Chapter 12 explains the role of macros in operations on generalized variables.
    • Chapter 13 shows how macros can make programs run faster by shifting computation to compile-time.Chap- ter 13 shows how macros can make programs run faster by shifting computation to compile-time.
    • Chapter 14 introduces anaphoric macros, which allow you to use pronouns in your programs.
    • Chapter 15 shows how macros provide a more convenient interface to the function-builders defined in Chapter 5.
    • Chapter 16 shows how to use macro-defining macros to make Lisp write your programs for you.
    • Chapter 17 discusses read-macros.
    • Chapter 18, macros for destructuring.
• Embedded Languages

  With Chapter 19 begins the fourth part of the book, devoted to embedded languages.

  • Chapter 19 introduces the subject by showing the same program, a program to answer queries on a database, implemented first by an interpreter and then as a true embedded language.
  • Chapter 20 shows how to introduce into Common Lisp programs the notion of a continuation, an object representing the remainder of a computation. Continuations are a very powerful tool, and can be used to implement both multiple processes and nondeterministic choice.
  • Chapters 21 and 22: Embedding these control structures in Lisp
  • Chapters 23 and 24 present two embedded languages which show that nondeterminism lives up to its promise: a complete ATN parser and an embedded Prolog which combined total about 200 lines of code.

    These programs are not short because they depend on programming tricks, but because they’re written using Lisp the way it’s meant to be used. The point of Chapters 23 and 24 is not how to implement ATNs in one page of code or Prolog in two, but to show that these programs, when given their most natural Lisp implementation, simply are that short. The embedded languages in the latter chapters provide a proof by example of the twin points with which I began: that Lisp is a natural language for bottom-up design, and that bottom-up design is a natural way to use Lisp.

• Object-Oriented Programming

  The book concludes with a discussion of object-oriented programming, and particularly CLOS, the Common Lisp Object System. By saving this topic till last, we see more clearly the way in which object-oriented programming is an extension of ideas already present in Lisp. It is one of the many abstractions that can be built on Lisp.

• Notes and Appendix

  A chapter’s worth of notes begins on page 387. The notes contain references, additional or alternative code, or descriptions of aspects of Lisp not directly related to the point at hand. Notes are indicated by a small circle in the outside margin. There is also an Appendix (page 381) on packages.