Programming Clojure, 3rd Edition

Vars, Bindings, and Namespaces

One of the most important tools in a programming language is the ability to name and remember values or functions for later use. In Clojure, a namespace is a collection of names (symbols) that refer to vars. Each var is bound to a value. Let’s consider vars more closely.

Vars

When you define an object with def or defn, that object is stored in a Clojure var. For example, the following def creates a var named user/foo:

(def foo 10)
-> #'user/foo

The symbol user/foo refers to a var that is bound to the value 10. If you ask Clojure to evaluate the symbol foo, it will return the value of the associated var:

foo
-> 10

The initial value of a var is called its root binding. Sometimes it’s useful to have thread-local ...