Programming Clojure, 2nd Edition

Flow Control

Clojure has very few flow control forms. In this section, you will meet if, do, and loop/recur. As it turns out, this is almost all you will ever need.

Branch with if

Clojure’s if evaluates its first argument. If the argument is logically true, it returns the result of evaluating its second argument:

(defn is-small? [number]
  (if (< number 100) "yes"))

(is-small? 50)
-> "yes"

If the first argument to if is logically false, it returns nil:

(is-small? 50000)
-> nil

If you want to define a result for the “else” part of if, add it as a third argument:

(defn is-small? [number]
  (if (< number 100) "yes" "no"))

(is-small? 50000)
-> "no"

The when ...