I haven't used an effect manager for this because I haven put in the time needed to learn how to create effect managers. :)
If what I've shown here can be accomplished with an effect manager then that's the way it should be done. :) On Wed, Jun 1, 2016 at 10:21 AM, James Wilson <jam...@gmail.com> wrote: > Thanks, that looks like basically exactly what I'd have guessed :) It's > super useful seeing an actual code sample with these ideas in. > > One thing I wonder now is; why not use an effect manager for this? It > basically seems to fit the exact same space (allows you to create a custom > Req like thing that can be mapped and batched and passed up the component > hierarchy - except that it's just a Cmd instead and plays nice with other > Cmds; allows you to maintain and update state (the cache) as you go; allows > you to "convert" Reqs to tasks to be run - just Cmds again now). In fact, > effect managers don't really seem to help you do anything other than what's > described here (plus a subscription side if you want it). Are there any > cons to using an effect manager here that you have in mind? > > On Tuesday, 31 May 2016 20:43:41 UTC+1, Peter Damoc wrote: >> >> The updating of the cache sounds to me like this: >> >> 1. if we have the info in cache, just supply the info without a HTTP GET >> 2. if we don't have the info in cache, return a different Msg that >> encapsulates the msg that requested the original information and the info >> required for the cache update. >> >> Here is a quick update of the code I've previously posted to include this >> caching mechanism. >> >> https://gist.github.com/pdamoc/d492ab58023926cd4d4950f12e5e170d >> >> >> >> >> On Tue, May 31, 2016 at 10:05 PM, James Wilson <jam...@gmail.com> wrote: >> >>> The key part that's not coded in the gist is the use of a cache/global >>> state object, however I think I see what you're getting at - pass back up >>> the chain a Req object, say, and at the top we can turn it into a Cmd >>> using, say, some top level global state as well as whatever other data we >>> need. This may lead to a request being made to the server or it may not. >>> >>> The other part of the puzzle is actually updating the cache when a >>> request is made. Req.toCmd for instance could return an updated GlobalState >>> so that it's able to cache "pending" states on values (so that we can avoid >>> duplicating requests). To update the cache when the response actually comes >>> in we could have toCmd return a Cmd.batch of 2 commands, one that will >>> fail/succeed and send a message to the component that initiated the Req, >>> and one that will send a message aimed at the top level cache itself. >>> >>> Thanks Peter, I'll definitely mull over this! >>> >>> On Tuesday, 31 May 2016 19:45:42 UTC+1, Peter Damoc wrote: >>>> >>>> ADT in Elm is one of its most powerful weapons. >>>> >>>> You could encapsulate your requests in a type and use this type at top >>>> level to fulfill them. >>>> >>>> For example: instead of returning Cmd msg you return some Req msg that >>>> can be turned into a Cmd msg at top level based on some context >>>> information. >>>> >>>> Here is a gist with a skeleton of how I view this implemented: >>>> https://gist.github.com/pdamoc/a47090e69b75433efa60fe4f70e6a06a >>>> >>>> I've sent the base of the URL as a simple String in `Req.toCmd` but you >>>> can imagine a more complex type holding all kind of information (e.g. >>>> cache, auth, etc ) . >>>> Also, I've kept the type of the Req simple (only saved the rest of the >>>> URL based on the user and the request) but one could use it to store all >>>> the info needed when you will turn the Req into a Cmd. >>>> >>>> >>>> >>>> >>>> >>>> >>>> On Tue, May 31, 2016 at 7:29 PM, James Wilson <jam...@gmail.com> wrote: >>>> >>>>> In Elm, each component basically has its own internal state (which is >>>>> actually all just a slice of one global model). In my app, I also want >>>>> global state that is independant of any components; for example a >>>>> clientside cache of various API responses (asset details - there could be >>>>> many thousands, user authentication status). >>>>> >>>>> I want any component to be able to call methods that make use of this >>>>> global state. For example, a method to obtain details for items in the >>>>> current view might first look at the global state to see if these items >>>>> are >>>>> cached. If they arent, the call would provide a Cmd to be issued that gets >>>>> the items (and puts them in the cache), while simultaneously updating the >>>>> state to indicate that they are being loaded (so that the same request >>>>> again from another component doesnt trigger another call to the backend). >>>>> If they are cached, they can be easily returned from there. A first shot >>>>> at >>>>> a signature might look something like: >>>>> >>>>> getItem : GlobalState -> ID -> Tag -> (GlobalState, Cmd msg) >>>>> >>>>> >>>>> >>>>> However we could partially apply functions that exist on some >>>>> globalState instantiation to hdie the initial state being passed in and >>>>> end >>>>> up with: >>>>> >>>>> state.items.getItem : ID -> Tag -> (GlobalState, Cmd msg) >>>>> >>>>> >>>>> >>>>> The downside of this approach is that I have to thread this state >>>>> through multiple calls that might make use of it, and thread it back up >>>>> explicitly through the update functions to get it back to the top. At the >>>>> top we'd then have something like (excuse any mistakes!): >>>>> >>>>> update msg model = case msg of >>>>> SubMsg m -> >>>>> let (newSubModel, subCmds, newGlobalState) = SubComponent.update >>>>> m model.subModel >>>>> in ({ model | state = newGlobalState, subModel = newSubModel}, >>>>> Sub.map SubMsg subCmds) >>>>> ... >>>>> >>>>> >>>>> An alternative approach is to hold this global state in an effect >>>>> manager, and so in the app you'd end up using the Cmd/Sub mechanism to ask >>>>> for things from the state and internally initiate API requests to update >>>>> the state as necessary. We'd end up with an API more like: >>>>> >>>>> getItem : ID -> Tag -> Cmd msg >>>>> >>>>> >>>>> or >>>>> >>>>> state.items.getItem : ID -> Tag -> Cmd msg >>>>> >>>>> >>>>> where the returned Cmd would either lead to an item being sent to the >>>>> component immediately via a cache (where Tag is a Msg type the component >>>>> knows about) or after it was obtained via some backend. This would make >>>>> all >>>>> retrieving of state async but seems to simplify the interface (perhaps at >>>>> the cost of more complexity in implementing the effect manager). >>>>> >>>>> Which approach do people think is best for working with global state >>>>> (neither is an option if you have a better way!)? Do you get away with not >>>>> needing this kind of thing (and if so, how)? I'd love to hear back, >>>>> especially from those that have had experience building larger apps in >>>>> Elm! >>>>> >>>>> -- >>>>> 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...@googlegroups.com. >>>>> For more options, visit https://groups.google.com/d/optout. >>>>> >>>> >>>> >>>> >>>> -- >>>> There is NO FATE, we are the creators. >>>> blog: http://damoc.ro/ >>>> >>> -- >>> 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...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> >> >> -- >> There is NO FATE, we are the creators. >> blog: http://damoc.ro/ >> > -- > 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. > -- There is NO FATE, we are the creators. blog: http://damoc.ro/ -- 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.
