Living Clojure

Chapter 1. The Structure of Clojure

Hello there. Do you have your Clojure REPL ready? If not, be sure to flip back to the Preface for information on getting it up and running so that you can explore the code examples as we go along in this chapter.

Beginning is always the hardest part. There are so many wonderful parts to Clojure that it is hard to figure out where to begin. When in doubt, always start simple. This chapter is about understanding the basic structure of a Clojure expression. So what is the simplest thing that we can enter into our Clojure REPL as code?

How about an integer?

Let’s try it together. Type your favorite integer into your REPL and see what happens:

42
;; -> 42

Here’s a rundown of what’s going on here:

1. The number 42 was typed into the REPL and the Enter key was hit.

2. The result of the expression was itself (meaning that it self-evaluated to 42).

3. The result of the expression was printed out. Here, we are showing that it is printed out by using the prefix ;; →.

In this simplest example, we have seen the basic mechanics of Clojure code evaluation. Clojure code is made up of expressions that are then evaluated to return a result. The simplest of these expressions are those that evaluate to themselves. They are called simple values or literals.

Baby Steps with Simple Values

We can type other kinds of Clojure code into the REPL that will also evaluate to itself. We have done an integer, so let’s try a decimal:

12.43
;; -> 12.43

What about a ratio?