promises and clojurescript

gistfile1.clj

(defn setup-midi!
  []
  (.then (.requestMIDIAccess js/navigator)
    (fn [midi-access]
      (.forEach (.-outputs midi-access)
          (fn [o]
           (let [name (.-name o)]
           (when (= "IAC"
                 (apply str (take 3 name)))
            (.then (.open o)
               (fn [o]
                (println "setting output to" (.-name o))
                (swap! app-state
                   (fn [s] (update-in s [:output] (constantly o)))))))))))))

Naive refactor.

(defn set-output [output]
   (swap! app-state (fn [s] (update-in s [:output] (constantly output))))

(defn reduce-output [output]
    (let [name (.-name output)]
       (when (= "IAC" (apply str (take 3 name)))
       (.then (.open o) set-output))

(defn handle-promise [midi-access]
    (reduce reduce-output (.-outputs midi-access)))

(defn setup-midi! []
   (.then (.requestMIDIAccess js/navigator) handle-promise))