Getting Clojure

A Global, Stable Place for Your Stuff

As we discovered all the way back in Chapter 1, def is about as simple as programming-language features come. You just hand it a symbol and a value:

def/examples.clj

(def title "Emma")

And it binds the symbol to the value. We’ve also seen that in contrast to the very local and temporary let, you use def for longer-lasting, more stable name-to-value bindings. Let’s start with the stable part: the rule is that a binding created with def will hang around until either you change it or the program terminates. This makes def perfect for constants:

;; Everyone's favorite universal constant.

(def PI 3.14)

;; Length of a standard book ID.

(def ISBN-LENGTH 13)

;; Company names are more or ...