(def circles (atom [{:x 1, :y 2, :x-speed 0.5, :y-speed 0.5}
                    {:x 3, :y 4, :x-speed 0.5, :y-speed 0.5}]))


(swap! circles (fn [v] (map (fn [c] (assoc c
                                           :x (+ (:x c) (:x-speed c))
                                           :y (+ (:y c) (:y-speed c)))) v)))