Basics in

About Basics

In Clojure, binding a value to a name is referred to as a var. Top-level (global) vars are similar to constants in other languages, but are commonly redefined to facilitate dynamic development.

Top-level vars are defined using def:

(def fingers 10)

You can use the core functions for operations on numbers to perform arithmetic on values.

The defn macro can be used to define a function taking zero or more arguments. A function always returns the result of the last expression in its body.

(defn add [x y]
  (+ x y))

Invoking a function is done by specifying its name and passing arguments for each of the function's parameters.

(def five (add 2 3))

Functions and values in Clojure can only be used after they have been defined. Using it before it has been defined results in a compile error.

;; Compile error as `add` has not yet been defined
(def seven (add 3 4))

(defn add [x y]
  (+ x y))

In Clojure, whitespace has no significance other than formatting.

Clojure functions and vars are organized in namespaces. A namespace groups related functionality and is defined using the ns macro:

(ns calculator)

(def pi 3.14)

(defn add [x y]
  (+ x y))

Clojure supports two types of comments. Single line comments are preceded by ; and the comment form is used to prevent evaluation of everything between (comment and ).