Hello-Macro in Clojure

If define the unless as function like this,

(defn unless [expr form] (if expr nil form))

Does that work?

(unless false (println "this should print"))
  => this should print
(unless true (println "this should not print"))
  => this should not print

Obviously the answer is no.

The reason is Clojure evaluates all the arguments before passing them to a function, so the println is called before unless ever sees it. So it seems Clojure is applicative order evaluation, but not normal order evaluation. (SICP exe. 1.5)

Therefore Macro.

(defmacro unless [expr form] (list 'if expr nil form))