Introduce attemptEach to run concurrently a List ConcurrentTask

[mpizenberg]

The rationale behind this new attemptEach function is to make it easier to run multiple tasks concurrently without having to synchronize them with a function like batch. This is mostly useful to run a bunch of independent tasks concurrently.

Let me know what you think, and don’t hesitate to change anything in the PR.

[andrewMacmurray]

Ok, finally aiming to get a bunch of these helpers merged now. Thanks for your input on this. Would you mind rebasing your branch on latest main and updating a couple of things?

I don't think it's useful for attemptEach to return a List (Cmd msg)- Cmds are opaque and there's not a lot you can do with them other than run them, so we might as well batch them in the helper. Could you modify the function to something like:

attemptEach :
    { pool : Pool msg
    , send : Decode.Value -> Cmd msg
    , onComplete : Response x a -> msg
    }
    -> List (ConcurrentTask x a)
    -> ( Pool msg, Cmd msg )
attemptEach options =
    List.foldl
        (\task ( pool_, cmds ) ->
            task
                |> attempt { options | pool = pool_ }
                |> Tuple.mapSecond (\nextCmd -> Cmd.batch [ nextCmd, cmds ])
        )
        ( options.pool, Cmd.none )

We can probably simplify the doc comment too, what about:

{-| Start a list of `ConcurrentTask`s. This is identical to [attempt](ConcurrentTask#attempt) except with a `List` of tasks.

    Use this when you don't need to wait explicitly for all the tasks to finish.

-}

Let me know if you don't have time for this and I can get it merged separately.

[mpizenberg]

I’ve made the rebase and most suggested changes. Tiny diff is I still accumulates the list of commands and batch at the end. It feels a bit too wrong for my ocd to wrap batch a list of 2 elements at each step. But don’t hesitate to modify if you prefer the other way.

[andrewMacmurray]

Looks good, pushed a small fixup to make the docs format nicely.