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(def the-world (ref "hello"))
(def bizarro-world (ref {}))
"In the beginning, there was a word"
(= "hello" (deref the-world))
"You can get the word more succinctly, but it's the same"
(= "hello" @the-world)
"You can be the change you wish to see in the world."
(= "better" (do
(dosync (ref-set the-world "better"))
"Alter where you need not replace"
(= "better!!!" (let [exclamator (fn [x] (str x "!"))]
(alter the-world exclamator)
(alter the-world exclamator)
(alter the-world exclamator))
"Don't forget to do your work in a transaction!"
(= 0 (do (dosync (ref-set the-world 0) )
"Functions passed to alter may depend on the data in the ref"
(= 20 (do
(dosync (alter the-world #(+ % 20)))))
"Two worlds are better than one"
(= ["Real Jerry" "Bizarro Jerry"]
(ref-set the-world {})
(alter the-world assoc :jerry "Real Jerry")
(alter bizarro-world assoc :jerry "Bizarro Jerry"))
[(:jerry @the-world) (:jerry @bizarro-world)])))