Hi Sam,
A nice late night exercise...
Not very practical, but if you want a safe transaction-free operation
on an atom which returns whether it was changed, you can perhaps hack
it by embedding the change state into the atom itself:
(def a (atom {:value 45 :changed? false}))
(defn update-and-check-whether-modified?
[update-fn]
(:changed?
(swap! a (fn [{v :value _ :changed?}]
(let [new-v (update-fn v)]
(if (== v new-v)
{:value new-v :changed? false}
{:value new-v :changed? true}))))))
(update-and-check-whether-modified? (fn [x] (+ x 1)))
(update-and-check-whether-modified? (fn [x] 70))
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