Moore machine using atom

moore.clj

(defn make-transitions [& states]
  (let [statemap 
        (zipmap
          (map str states) 
          (rest (conj (vec states) (first states))))]
    (fn [state] (statemap (str state)))))

(def moore-machine (atom :stopped))
(def transitions (make-transitions :starting :started :stopping :stopped))

(swap! moore-machine transitions) ;; :starting
(swap! moore-machine transitions) ;; :started
(swap! moore-machine transitions) ;; :stopping
(swap! moore-machine transitions) ;; :stopped