example_of_atom_swap.clj

(def players
  [{:id 1 :health 100} {:id 2 :health 90}])
  
(def game
  {:players players})

(def current-game
  (atom game))

(defn kill-player
  [player]
  (assoc player :health 0))

(defn kill-players
  [players]
  (map kill-player players))

(defn kill-players!
  [game-atom]
  (swap! game-atom update-in [:players] kill-players))

(kill-players! current-game)