Checked the current implementation of Cmd.batch and it appears sequential (`mailbox.push`). Ordering guarantees are not documented so I suppose they shouldn't be depended on. But otherwise, the one I coded above that guarantees Act doesn't change the model and Evt doesn't have effects would work.
On Thursday, August 11, 2016 at 6:33:39 PM UTC-5, Kasey Speakman wrote: > > Yes, that's why I said back to square one if Cmd.batch isn't ordered. The > only thing this is guaranteeing (and the only intended guarantee) is that > the messages which only update the model are separated from the ones which > cause effects. The ones which cause effects produce ones which update the > model, same as always. > > It occurs to me that some of the benefit of event sourcing the UI could be > gained by adding features to the TTD, since it has the magic which ignores > Cmds on replay. Some are already listed as ideas at > http://debug.elm-lang.org/. I'd still have to keep the messages in my > model and provide a way for the user to transmit them in a bug report. But > if I could load them in the TTD, that would make repro a snap. > > On Thursday, August 11, 2016 at 5:22:05 PM UTC-5, OvermindDL1 wrote: >> >> Isn't `doSideEffects` basically just the current `update` function >> though? Except it is returning a list of changes (via message) to perform >> to a model instead of doing it in-place? What is this saving precisely? >> >> >> >> On Thursday, August 11, 2016 at 4:05:57 PM UTC-6, Kasey Speakman wrote: >>> >>> Actually, I'd probably use a List instead of Maybe on the immediately >>> returned event(s). >>> >>> doSideEffects : Act -> Model -> (List Evt, Cmd Evt) >>> doSideEffects act model = >>> case act of >>> UpdateCustomer customer -> >>> ( [ CustomerUpdateRequested ] >>> , callServerWithCustomer customer >>> ) >>> >>> ... >>> >>> updateModel : Evt -> Model -> Model >>> ... -- implementation as previous >>> >>> update : Msg -> Model -> (Model, Cmd Msg) >>> update msg model = >>> case msg of >>> Action act -> >>> let >>> (events, command) = doSideEffects act model >>> in >>> (List.foldr updateModel model events, Cmd.map Evt command) >>> >>> Event evt -> >>> (updateModel evt model, Cmd.none) >>> >>> >>> >>> On Thursday, August 11, 2016 at 4:26:03 PM UTC-5, Kasey Speakman wrote: >>>> >>>> Yes, that was the goal. That way the UI state is utterly deterministic >>>> / reproducible in isolation of all outside services. >>>> >>>> That's a good point on the race conditions. I only use Cmd.batch >>>> because it's the facility that came to mind. (I'm still getting acquainted >>>> with Elm.) I don't know if Cmd.batch makes any ordering guarantee. >>>> >>>> If not we'd be more or less back to square one. Abuse `update` to do >>>> both things. >>>> >>>> doSideEffects: Act -> Model -> (Maybe Evt, Cmd Evt) >>>> doSideEffects act model = >>>> case act of >>>> UpdateCustomer customer -> >>>> (Just CustomerUpdateRequested, callServerWithCustomer customer) >>>> >>>> ... >>>> >>>> updateModel: Evt -> Model -> Model >>>> ... -- implementation as previous >>>> >>>> maybeUpdateModel: Maybe Evt -> Model -> Model >>>> maybeUpdateModel evtOpt model = >>>> case evtOpt of >>>> Nothing -> >>>> model >>>> >>>> Just evt -> >>>> updateModel evt model >>>> >>>> update : Msg -> Model -> (Model, Cmd Msg) >>>> update msg model = >>>> case msg of >>>> Action act -> >>>> let >>>> (eventNow, command) = doSideEffects act model >>>> in >>>> (maybeUpdateModel eventNow model, Cmd.map Evt command) >>>> >>>> Event evt -> >>>> (updateModel evt model, Cmd.none) >>>> >>>> So this should apply an event immediately if one is needed for the >>>> action. But it still keeps the model updating events separate. >>>> >>>> These immediate events would be seen by a userland event-store >>>> implementation (which is underneath updateModel), but I bet the TTD >>>> wouldn't see it since it doesn't come from Elm. >>>> >>>> On Thursday, August 11, 2016 at 3:43:36 PM UTC-5, OvermindDL1 wrote: >>>>> >>>>> So you really are wanting to hard device events into two different >>>>> ones, those that can *only* alter the model, and those that can *only* >>>>> send >>>>> commands (which may call ones that alter the model). Unsure if it might >>>>> actually happen but might have to take into account possible race >>>>> conditions for if other messages appear before your other expected ones >>>>> are >>>>> processed through? Easier to do that atomically all at once? >>>>> >>>>> >>>>> On Thursday, August 11, 2016 at 2:25:22 PM UTC-6, Kasey Speakman wrote: >>>>>> >>>>>> doSideEffects above would also have to map Cmd Evt to Cmd Msg. >>>>>> >>>>> -- You received this message because you are subscribed to the Google Groups "Elm Discuss" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
