ClojureScript - assoc is not working inside a promise

Question

I have an array of art pieces. I want to find the route length and associate it with each art pieces.

My code will look like:

(defn load-art-routes [art-list ctx]
 (doall (map-indexed (fn [index art]
   (let [user-location (select-keys (:coords (sub> ctx :geolocation)) [:latitude :longitude])
         art-location (:geoLocation art)]
       (->> (map-request {:origin (str (:latitude user-location) "," (:longitude user-location))
                     :destination (str (:lat art-location) "," (:lon art-location))
                     :mode (name (sub> ctx :transition-mode))})
             (p/map (fn [data]
                   (let [route-length (ocall js/Math "round" (/ (get-in data [:routes 0 :legs 0 :distance :value]) (* 0.621371192 1000)) 2)
                         route-duration (ocall js/Math "floor" (/ (get-in data [:routes 0 :legs 0 :duration :value]) 60))]
                     (js/console.log "load-art-routes route-length " route-length")
                     (assoc art :route-length route-length))))
             (p/error (fn [error]
                       (util/log (str "GOOGLE DIRECTIONS API ERRORS" params) error)
                       ))))) art-list))
                       art-list)
(defn map-request [params]
 (when params
   (let [endpoint google-directions-api-endpoint]
     (->> (make-get-req (str endpoint "&" (encode-query-params params))
                        {})
          (p/map (fn [data]
                   (util/log "GOOGLE DIRECTIONS API " data)
                   data))
          (p/error (fn [error]
                     (util/log (str "GOOGLE DIRECTIONS API ERRORS" params ) error)
                     ))))))

The route length calculation is correct but, assoc is not working. It is not actually associating it. I don't know what the issue is. Can anyone help me?

Answer 1

Please simplify this example! In the process, you will discover the problem.

First, update your question to include the require that shows what p/map , p/error , etc are. Also, put map-request before load-art-routes just like it must be in your source file.

Then, you should start by removing the thread-last ->> operator and use let with names for intermediate values:

(let [aa (map-request ...)
      bb (p/map (fn [data] ...)   aa)
      cc (p/error (fn [error] ...) bb) ]
  <bb or cc here?> )

My suspicion is that your p/error call is swallowing the results of p/map and returning nil .

Answer 2

This looks like you are trying to write "mutable" code.

Reformatting the code and fixing one error makes this more obvious:

(defn load-art-routes [art-list ctx]
  (doall (map-indexed (fn [index art]
                        (let [user-location (select-keys (:coords (sub> ctx :geolocation)) [:latitude :longitude])
                              art-location (:geoLocation art)]
                          (->> (map-request {:origin (str (:latitude user-location) "," (:longitude user-location))
                                             :destination (str (:lat art-location) "," (:lon art-location))
                                             :mode (name (sub> ctx :transition-mode))})
                               (p/map (fn [data]
                                        (let [route-length (ocall js/Math "round" (/ (get-in data [:routes 0 :legs 0 :distance :value]) (* 0.621371192 1000)) 2)
                                              route-duration (ocall js/Math "floor" (/ (get-in data [:routes 0 :legs 0 :duration :value]) 60))]
                                          (js/console.log "load-art-routes route-length " route-length)
                                          (assoc art :route-length route-length))))
                               (p/error (fn [error]
                                          (util/log (str " GOOGLE DIRECTIONS API ERRORS " params) error)
                                          ))))) art-list))
  art-list)

load-art-routes simply returns the original art-list and kicks of some work in promises. These promises only update their versions of the list but given that we are using immutable data structures the returned art-list themselves remain unchanged. There is also a suspicious second art-list in the p/error call?

You'll probably want to restructure this to something that either returns a Promise or accepts a callback that will be called once all route-length have been computed.