マウスを押している時のみのmoveイベントだけ取るようなtransducers

mouse-drag-transducers.clj

(def events [:move :press :move :move :release :press :release :press :press :move :move :move :release :move :move])
(defn make-drag-filter-fn []
  (let [pressed? (atom false)]
    (fn [event]
      (cond
        (and @pressed? (= :move event)) true
        (= :press event) (do (reset! pressed? true) false)
        (= :release event) (do (reset! pressed? false) false)
        :else false))))

(def xf (filter (make-drag-filter-fn)))
;;(eduction xf events)