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 [email protected]. For more options, visit https://groups.google.com/d/optout.
