stm-demo.clj

(def player (ref {:health 500 :attack 10 :items #{}}))
(def mob1   (ref {:health 100 :attack 2  :items #{"big-banana"}}))
(def mob2   (ref {:health 100 :attack 4  :items #{"banana"}}))


(defn attack! [attacker enemy]
  (dosync
    (let [attacker-value (:attack @attacker)
          enemy-value (:attack @enemy)]
      (alter enemy    update :health - attacker-value)
      (alter attacker update :health - (/ enemy-value 2)))))


(defn loot! [to from]
  (dosync
    (when-let [item (first (:items @from))]
      (alter to update :items conj item)
      (alter from update :items disj item))))


(comment 
  (attack! player mob1)
  (attack! player mob2)
  (loot!  player  mob2))