Update and clarify in changes document.

src/re_frame/fx.cljs

@@ -0,0 +1,112 @@
+(ns re-frame.fx
+  (:require [re-frame.router :refer [dispatch]]
+            [re-frame.db :refer [app-db]]
+            [re-frame.loggers    :refer [console]]))
+
+
+
+;; -- Registration ------------------------------------------------------------
+;;
+(def ^:private id->handler-fn  (atom {}))
+
+(defn lookup-handler
+  [event-id]
+  (get @id->handler-fn event-id))
+
+
+(defn clear-handlers!
+  "Unregister all effects handlers"
+  []
+  (reset! id->handler-fn {}))
+
+
+(defn register
+  "register a handler fn for an effect."
+  [event-id handler-fn]
+  (when (contains? @id->handler-fn event-id)
+    (console :warn "re-frame: overwriting an effects handler for: " event-id))   ;; allow it, but warn.
+  (swap! id->handler-fn assoc event-id handler-fn))
+
+
+;; -- Standard effets ---------------------------------------------------------
+
+
+(defn dispatch-helper
+  [effect]
+  (cond
+    (list? effect)   (map dispatch effect)
+    (vector? effect) (dispatch effect)
+    :else (console :error "re-frame: expected :dispatch effect to be a list or vector, but got: " effect)))
+
+;; Example:
+;; {:dispatch-later {200  [:event-id "param"]    ;;  in 200ms do this: (dispatch [:event-id "param"])
+;;                   100  [:also :this :in :100ms]
+;;                   250  (list [:do ] [:all ] [:three ])}
+;;
+(register
+  :dispatch-later
+  (fn [effect]
+    (doseq  [[ms events] effect]
+        (js/setTimeout #(dispatch-helper events) ms))))
+
+(register
+  :dispatch
+  (fn [effect]
+    (dispatch-helper effect)))
+
+
+;;
+;; {:forward-events  {:listen      :an-id-for-this-listner
+;;                    :events      #{:event1  :event2}
+;;                    :dispatch-to [:eid "eg. param"]}     ;; the forwared event will be conj to the end of the dispatch.
+;;
+;; {:forward-events  {:unlisten :the-listner-id-I-originally-supplied}}
+;;
+(register
+  :forward-events
+  (let [id->listen-fn (atom {})
+        process-entry (fn [{:keys [listen events dispatch-to unlisten]}]
+                        (if (some? unlisten)
+                          (do
+                            (unregister XXXX)
+                            (swap! id->listen-fn dissoc unlisten))))]
+
+
+    (fn [val]
+      (cond
+        (map? val) (process-entry m)
+        (list? val) (doseq []))
+      (do-dispatches (:dispatch world)))))
+
+
+(register
+  :db
+  (fn [world]
+    (if-let [db (:db world)]
+      (reset! app-db db))))
+
+;; -- Middleware --------------------------------------------------------------
+
+;; XXX a coeffect for jsDate ?
+;; XXX add metadata saying it is fx.
+;; XXX add config
+;; XXX world or branch ??  Return world?
+;; XXX ordering
+;; XXX review other standard middleware
+;; XXX write a gist for :http
+;; XXX think about an undo effect
+;;     :undo
+
+
+(defn fx
+  [handler]
+  (fn fx-handler
+    [app-db event-vec]
+    (let [world   {:db @app-db}
+          result (handler world event-vec)
+          effects (-> result (dissoc :db) keys)
+          handlers (map lookup-handler effects)
+          retult' (reduce #(%2 %1) result handlers)]
+
+      (if-let [db (:db result)]
+        (reset! app-db db)))))