effects-handling.clj

(defmulti control (fn [action] action))

(defmethod control :init [_ _ _]
  {:state {:count 0}}) ;; <= initial state effect

(defmethod control :inc [_ _ state]
  {:state (update state :count inc)}) ;; <= increment state effect

(defmethod control :load [_ [id] _]
  {:http {:uri (str "/api/count/" id)
          :on-success :load-ready
          :on-fail :load-fail}}) ;; <= HTTP effect

(defmethod control :load-fail [_ [error] state]
  {:state (assoc state :error error)}) ;; <= load error state effect

(defmethod control :load-ready [_ [response] state]
  {:state (assoc state :count response)}) ;; <= load success state effect

(defmethod control :persist [_ _ state]
  {:local-storage {:method :set
                   :key :my-app/counter
                   :data (-> state clj->js js/JSON.stringify)}}) ;; <= persist localStorage effect

(defmethod control :read-persist [_ _ _]
  {:local-storage {:method :get
                   :key :my-app/counter
                   :on-read :read-persist-ready}}) ;; <= read persist localStorage effect

(defmethod control :read-persist-ready [_ [data] state]
  {:state (->> data js/JSON.parse js->clj)}) ;; <= read persist localStorage success effect

;; ===========================

(def r
  (scrum/reconciler
    {:state (atom {})
     :controllers {:counter counter/control}}
     :effects {:http effects/http
               :local-storage effects/local-storage}))

(scrum/broadcast-sync! :init)

(scrum/dispatch! :counter :load 5)

;; ===========================

(defn http [reconciler controller {:keys [uri on-success on-fail]}]
  (-> (httpurr/get uri)
      (p/then #(scrum/dispatch! reconciler controller on-success %))
      (p/catch #(scrum/dispatch! reconciler controller on-fail %))))

(defn local-storage [reconciler controller {:keys [method key data on-read]}]
  (case method
    :set (js/localStorage.setItem (str key) data)
    :get (->> (js/localStorage.getItem (str key)) (scrum/dispatch! reconciler controller on-read))
    nil))

Line 18 why not simply return response ? In this proposal, the control controller isn't responsible directly for the state at the key :counter ? What is the value of the state parameter in the controller methods ?