re-frame event loosely mimicking clojure 1.11's iteration

iteration.cljs

;; recur-event - dispatch vector for when target isn't reached
;; :root-path - Where is this iteration state to be kept in the app-db?
;; :unwrap - pre process step-ret. Identity by default. Example: parse json and get body key of response
;;          unwrap output is input for nextf, reachedp, updatef, somep
;; :somep - Are there more items in this request? If not, consider this to be the end of available items
;; :nextf - Get next cursor value
;; :updatef - Update values - takes old values and output of unwrap, update iteration values in app-db
;; :reachedp - Did the cursor reach the desired item? passed ret val of nextf, is nextf by default
(rf/reg-event-fx
 ::iteration
 (fn [{:keys [db]} [_ recur-event opts step-ret]]
   (let [{:keys [nextf updatef unwrapf somep reachedp root-path]
          :or {unwrapf identity somep identity reachedp nextf}}
         opts

         stepv (unwrapf step-ret)
         nextv (nextf stepv)
         more? (somep stepv)

         next-db (if more?
                   ;; Values exist
                   (-> db
                       (assoc-in (conj root-path :next) nextv)
                       (update-in (conj root-path :values) updatef stepv))

                   ;; Values absent
                   (assoc-in db (conj root-path :terminated?) true))]

     (cond-> {:db next-db}
       (and more? (reachedp nextv))
       (assoc :dispatch recur-event)))))


;; Example of this being used on a pathom endpoint
(re-frame/reg-event-fx
 ::get-gallery-image
 (fn [{:keys [_db]} [event gallery-id image-id]]
   {:request {:name event
              :params {:context {:gallery/id gallery-id}
                       :query ['({:gallery/images [:filepath]} {:cursor cursor})
                               :gallery/images-cursor]}
              :on-success [::iter/iteration
                           [event gallery-id image-id]
                           {:root-path [:galleries gallery-id :iteration]
                            :nextf :gallery/images-cursor
                            :updatef into
                            :somep (comp empty? :gallery/images)
                            :reachedp #(< image-id %)}]
              :on-failure [::get-gallery-images-failure]}}))