10. Numbers, Characters, and Strings

While functions, variables, macros, and 25 special operators provide the basic building blocks of the language itself, the building blocks of your programs will be the data structures you use. As Fred Brooks observed in The Mythical Man-Month, “Representation is the essence of programming.”1

And these built-in types are just the beginning. They’re defined in the language standard so programmers can count on them being available and because they tend to be easier to implement efficiently when tightly integrated with the rest of the implementation. But, as you’ll see in later chapters, Common Lisp also provides several ways for you to define new data types, define operations on them, and integrate them with the built-in data types.

In this chapter, I’ll cover the built-in “scalar” data types: numbers, characters, and strings. Technically, strings aren’t true scalars—a string is a sequence of characters, and you can access individual characters and manipulate strings with a function that operates on sequences. But I’ll discuss strings here because most of the string-specific functions manipulate them as single values and also because of the close relation between several of the string functions and their character counterparts.