Simple example of atoms and atomic updates based on an example from Chapter 4 of Programming Clojure by Emerick, et al.

age-person.clj

(ns examples.age-person)

;; Based on an example from Chap 4 of Programming Clojure
;; by Emerick, et al
(defmacro futures
  [n & exprs]
  (vec (for [_ (range n)
             expr exprs]
         `(future ~expr))))

(defmacro wait-futures
  [& args]
  `(doseq [f# (futures ~@args)]
           @f#))

(def chris (atom {:name "Chris" :age 40 :wears-glasses? false}))

;; Note that because comp goes "right to left" we do the glasses check first 
;; and *then* increment the age. That means that we'll first wear glasses at
;; age 46.
(defn age-person [person]
  (swap! person (comp #(update-in % [:age] inc)
                      #(do (Thread/sleep (rand-int 100)) %)
                      #(assoc % :wears-glasses? (or (println "\tTrying when they are " (:age %))
                                                    (:wears-glasses? %)
                                                    (>= (:age %) 45)))
                      )))

(wait-futures 10 (do 
                   (age-person chris)
                   (println "Succeeded, now Chris is " @chris)
                   ))