Chapter 16. The Magic of Lisp Macros

Macro programming allows you to mess around inside your Lisp compiler/interpreter to turn Lisp into your own custom programming language. When faced with a difficult programming challenge, many experienced Lispers will first ask themselves, “What programming language could I use to make this problem easy to solve?” Then they’ll use macros to convert Lisp into that language!

No other programming language possesses such a simple and comprehensive macro system. One can even argue that it would be impossible to add this feature to other programming languages, for a simple reason: The Lisp languages are the only ones in which computer code and program data are made out of the same “stuff.” As discussed many times in this book, the fundamental structures for storing data in Lisp are symbols, numbers, and lists, which are made of cons cells. Similarly, the code of a Lisp program is made out of these same basic building blocks. As you’ll see in this chapter, this symmetry between code and data in Lisp is the magic that makes the Lisp macro system possible.