refactor.clj

(defn computer-down? [{{computer-y :y} :computer 
                       {ball-y :y} :ball player-height :player-height :as state}]
  (and  (> (- computer-y 20) ball-y) (>= (- computer-y (/ player-height 2)) 0)))
  
;; vs.

(defn computer-down? [{:keys [ball computer] :as st}]
  (let [cy (:y computer)]
    (and (> (- cy 20) (:y ball))
         (>= (- cy (/ (:player-height st) 2)) 0))))