Ability to "fail to start"

[blaix]

Currently if your application model depends on the result of a task that can fail, you need to keep a Maybe on the model, because you have to call Node.startProgram with an instance of your model no matter what. If there was a way to explicitly not start the program, you could avoid the Maybe and fail directly in init. For example:

getSecureContext : Task Never (Maybe Crypto.SecureContext)
getSecureContext =
    -- Turn fail-able task into one that always resolves. 
    ...

init env =
    Init.await getSecureContext <| \maybeSecureContext ->
        when maybeSecureContext is
            Nothing ->
                Node.failToStart "Failed to get secure context."
            Just secureContext ->
                Node.startProgram
                    { model =
                        { secureContext = secureContext -- don't need a Maybe
                        ...

Probably will want something similar for Browser.