Arities ================================================== [test then] [test then else] Docstring ================================================== Evaluates test. If logical false, evaluates and returns then expr, otherwise else expr, if supplied, else nil.
(defmacro if-not
"Evaluates test. If logical false, evaluates and returns then expr,
otherwise else expr, if supplied, else nil."
{:added "1.0"}
([test then] `(if-not ~test ~then nil))
([test then else]
`(if (not ~test) ~then ~else)))
(if-not (zero? 0) :then :else)
;; => :else
;; See examples for "if" explaining Clojure's idea of logical true
;; and logical false.
(defn has-neg [coll]
(if-not (empty? coll) ;; = (if (not (empty? coll)) ...
(or (neg? (first coll)) (recur (rest coll)))))
;; => #'user/has-neg
(has-neg [])
;; => nil
(has-neg [1 2 -3 4])
;; => true