>
> I'm trying to rebuild the successor to some past systems in Elm and one
> thing we learned on those systems was that to get good performance it was
> critical that we prioritize HTTP fetches so that we didn't ask for the low
> priority items at the same time as the high priority items. From a
> correctness standpoint, the particular fetches are a local problem and the
> Elm architecture provides a reasonable way to route those. But the
> prioritization is a global problem. To go with that, I need cancelation
> support because that's the other key piece in getting responsiveness and
> what that means in practice is that if something hasn't left the queue yet,
> I need a way to cancel it.
>
Okay, now we're getting somewhere!
So you have a specific problem where you need a global queue for
dispatching HTTP requests according to your applications' particular
business logic.
Here's how I would approach this if I had these same design constraints. I
would add something like this to my model:
requestQueue : Dict RequestId { order : Int, request : Task Never Msg }
Then I'd introduce a function to enqueue messages with a particular
priority level that determines the order value.
I'd also introduce a Msg called Dispatch that pulls the next thing off the
queue (sorting Dict.values by the order field) and uses Task.perform to run
the HTTP request.
To allow canceling, I'd add this to my top-level Msg:
| CancelRequest RequestId
This is what I would do if I had your particular business need. Seems
pretty reasonable!
I also think it would be no problem to introduce this to an existing Elm
application after the fact. Just start by deleting your dependency on
elm-http, and the compiler will immediately tell you every single place you
were doing HTTP "the old way." Go through and transition those direct HTTP
calls to use a stubbed-out implementation of "the new way," and then
finally reintroduce the elm-http dependency to make the queue work for real!
I'll also note that this use case seems very specific to your application.
I would avoid trying to overgeneralize this into any kind of pattern that
others should follow. :)
--
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.
