Effect functions do not trigger as described in documentation (app tutorial)

[avescodes]

The documentation for pedestal states, that effect functions configured in dataflow description under :effect key should trigger when value in data model at configured path changes. However, i'm experiencing different behavior, such that all effect functions are called first time even when there is no data (and therefore no change) at configured path.

Consider following code:

(defn init-app []
  [{:app
     {:control {:menu {:value nil}}
      :new-workflow {:form
                     {:transforms 
                      {:send [{msg/type :set-sending msg/topic [:app :new-workflow :form] (msg/param :value) {}}]}}}
      :workflows {:value nil}
      :instances {:value nil}
      :selected-workflow {:value nil}
      :selected-instance {:value nil}}}])

(def workflow-app
  {:version 2
   :transform [[:set-value [:**] set-value-transform]
                    [:set-sending [:**] set-sending]
                    [:clear-sending [:**] clear-sending]]
   :derive #{[{[:app :control :selected] :selected [:app :control :menu] :menu} [:app :control :menu] select-tab-menu :map]
             [{[:app :workflows] :workflows [:app :instances :*] :changed-instances} [:app :instances] add-wf-to-instance :map]
             [{[:app :workflows] :workflows [:app :selected-workflow] :workflow-id} [:app :selected-workflow] select-workflow :map]
             [{[:app :instances] :instances [:app :selected-instance] :instance-id} [:app :selected-instance] select-instance :map]}
   :effect #{[#{[:app :new-workflow :form :sending]} publish-new-workflow :single-val]}
   :emit [{:init init-app}
             [#{[:app :control :menu :*]
                 [:app :new-workflow :form :sending]
                 [:app :workflows :*]
                 [:app :instances :*]
                 [:app :selected-workflow :*]
                 [:app :selected-instance :*]} (app/default-emitter [])]]
   :focus {:add-workflow [[:app :control] [:app :new-workflow]]
              :list-workflows [[:app :control] [:app :workflows]]
              :list-instances [[:app :control] [:app :instances]]
              :detail-workflow [[:app :control] [:app :selected-workflow]]
              :detail-instance [[:app :control] [:app :selected-instance]]
              :default (get-focus-key initial-menu)}})

Even when there is no data at the path [:app :new-workflow :form :sending] at the initialisation, the function publish-new-workflow is called with nil argument for the first time, after that it works fine, and the function is called only when data at path [:app :new-workflow :form :sending] changes.

Operating System: Ubuntu 13.10 Saucy Salamander Leiningen version: Leiningen 2.3.3 on Java 1.7.0_45 Java HotSpot(TM) 64-Bit Server VM Pedestal version: 0.2.2-SNAPSHOT Steps to reproduce: Define dataflow with effect function under :effect key and configure the function to use the path in the data model with no starting data, observe how the function is called with nil value for the first time after building the dataflow and consuming effects.