explanation

lilactown Today at 5:22 PM
I remember someone in this channel talking about constructing effects data using function chaining; who was that? tell me your secrets again :stuck_out_tongue:
32 replies

p-himik  1 hour ago
If I understand you correctly, it was probably @emccue

emccue  1 hour ago
@lilactown refresh my memory a bit?

emccue  1 hour ago
I think i know what you are asking for, but i want to make sure before i go off

lilactown  1 hour ago
something about how you organize your events/effects, where instead of writing the effects in an event as data you use helper functions to construct the effects:
(rf/reg-event-fx
  ::something
  (fn [{:keys [db]} [_ foo bar]]
    (-> (do-thing {} foo)
        (do-another-thing bar)
        (do-one-last-thing))))
(edited)

emccue  43 minutes ago
yeah so the first bit is every event handler is a reg-event-fx for consistency

emccue  42 minutes ago
and we only ever return :db and :fx

emccue  42 minutes ago
for :fx, we have namespaces dedicated to them that look basically like this

emccue  41 minutes ago
(rf/reg-fx
  ::alert
  (fn [contents]
    (js/alert contents)))
(defn alert [contents]
  [[::alert contents]])
(defn alert-uppercase [contents]
  (alert (string/upper-case contents)))

emccue  40 minutes ago
so each "effect" is a function you call that returns a vector of vectors

emccue  40 minutes ago
{:fx (alert "abc")}

emccue  40 minutes ago
and if you want to combine fx, we have a helper function that concats them together

emccue  39 minutes ago
{:fx (fx/in-order
         (alert "abc")
         (http-req {...}))}
(edited)

emccue  38 minutes ago
then if we have some process that we want to re-use in multiple handlers that will update state and perform some effects, we make a function

emccue  38 minutes ago
(defn do-thing [db]
  {:db (inc db}
   :fx (alert-fx/alert "abc")})

emccue  37 minutes ago
and we have another helper that lets us compose functions that have the signature db -> {:db, :fx}

emccue  36 minutes ago
(rf/reg-event-fx
  ::abc
  (fn [{:keys [db]} [_ abc]]
    (let [process (compose-effect-fns
                             do-thing
                             (fn [db] {:db (* db 2)}))]
       (process db))))
(edited)

emccue  32 minutes ago
and for new stuff we aren't allowing dispatches within a handler - keeping dispatches to only stuff the user did or reactions to outside processes

emccue  32 minutes ago
beyond that nowadays its gotten to

emccue  31 minutes ago
(defevent abc
  [a b c]
  :handler
  (fn [{:keys [db]}]
    {:db (* db a b c)
     :fx (alert-fx/alert "AAA")}))

lilactown  31 minutes ago
how do you handle like, "do a network request and then update the app-db"?

emccue  30 minutes ago
which produces a constant event:abc equal to ::abc , a function abc, which when called will produce a vector you dispatch and a function handler:abc which is your re-frame handler

emccue  30 minutes ago
do you mean app-db updates you do as soon as you launch the request or when it comes back

emccue  22 minutes ago
(defevent successfully-did-thing
  [response]
  :handler
  (fn [{:keys [db]}]
    {:db (* db 2)}))
(defevent failed-to-do-thing
  [error]
  :handler
  (fn [{:keys [db]}]
    {:db (/ db 5)}))
(defevent do-thing
  [user-id]
  :handler
  (fn [{:keys [db]}]
    {:db (+ db 1)
     :fx (http-fx/request 
           {:uri "..." 
            :params {... user-id ... }
            :on-success successfully-did-thing
            :on-failure failed-to-do-thing})}))

emccue  22 minutes ago
(we re-wrote the normal :http-xhrio to support some stuff like functions for on-success, but same concept)

emccue  18 minutes ago
does that make sense?
:+1::skin-tone-2:
1


p-himik  16 minutes ago
@emccue That's at least the third time I see how you write extensively on this topic.
Have you considered making a blog post or at least a detailed gist about it? Would be easier to share, publicly improve upon, and discuss in a persistent manner that's not possible on this Slack.

emccue  12 minutes ago
eh? its a pattern we still haven't worked out all the issues with and are using as a tool to patch up a large codebase. The ideal end point might be a library other than re-frame because it explicitly goes against what I think is intended design

emccue  12 minutes ago
plus its literally just the way elm does stuff being forced onto re-frame - not without reason, but certainly without elegance

emccue  11 minutes ago
but yeah next time it comes up I'll try to make a gist
:+1::+1::skin-tone-2:
2


emccue  7 minutes ago
also i don't have a blog to put it on - i know that makes me a heretic

lilactown  4 minutes ago
a gist or something durable would be great for me! thanks for taking the time to write this down

lilactown  3 minutes ago
bouncing around meetings rn but I will digest and maybe ask a couple more qs in a bit