; Comments begin with a ;
(println "meow") ; => nil

; All built-in data structures are persistent and immutable.
(def george {:name "George Clooney"}) ; => #'user/george

; Though all data is immutable by default, side effects are adhoc.
(defn say-hi [who]
  (println (str "Hi " (:name who) "!"))
  (assoc who :greeted? true))

; Doesn't change george.
(say-hi george) ; => {:name "George Clooney"
                ;     :greeted? true}

; Many core functions for working with immutable data.
(apply + (distinct [12 8 12 16 8 6])) ; => 42

; Interop with C++ can happen *seamlessly*.
(defn sleep [ms]
  (let [duration (cpp/std.chrono.milliseconds ms)]
    (cpp/std.this_thread.sleep_for duration)))