Hmm, I'd be curious if you could whip up a full compileable example, say a Multi-Counter project example we could paste into elm-try. Perhaps mark things that are boilerplate and could be hoisted out to a parent library too so we can ignore those? :-)
On Friday, August 12, 2016 at 12:15:20 PM UTC-6, Kasey Speakman wrote: > > Skimming through the code, it looks like batch commands will happen in > order. The mentioned `mailbox.push` was from the Elm source code. > > Also, I fleshed out an example with both a clean separation and using > event sourcing. I posted it with some commentary on marcosh's github > <https://github.com/marcosh/marcosh.github.io/issues/1>. > > I like the terminology in this example much better than my previous > examples, especially because `Action` was a previous concept in Elm. > > type Act = Increment | Decrement > > type Fact = Incremented Int | Decremented Int > > type Msg = Perform Act | Apply Fact > > perform : Act -> Model -> Cmd Msg > > apply : Fact -> Model -> Model > > update : Msg -> Model -> (Model, Cmd Msg) > update msg model = > case msg of > Perform act -> > (model, perform act model) > > Apply fact -> > (apply fact model, Cmd.none) > > > The Facts here are also idempotent > <https://en.wikipedia.org/wiki/Idempotence> (no dependency on previous > values). That's not as important in this example, but can as its extended. > > On Friday, August 12, 2016 at 9:15:23 AM UTC-5, OvermindDL1 wrote: >> >> Will your pushed command appear after or before a potentially pushed >> 'other' command, say from an incoming port, or button click? That is the >> part I am not sure about yet (not read enough Elm internals 'quite' yet). >> >> On Thursday, August 11, 2016 at 6:31:06 PM UTC-6, Kasey Speakman wrote: >>> >>> 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 elm-discuss+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
