You could use this trick:
case (state, msg) of
(Displaying stuff, UpdateThis) -> ...
(Displaying stuff, UpdateThat) -> ...
(Loading, _) -> ...
_ -> ... {- only if needed -}
On Tuesday, 17 January 2017 15:03:05 UTC+1, Tomáš Znamenáček wrote:
>
> Hello!
>
> I have an app that loads some JSON from a website and displays it. The
> state of the app could be modelled a bit like this:
>
> type State =
> Loading |
> Displaying Stuff
>
> type alias Stuff = { … }
>
> Now I am writing the update function to handle messages:
>
> update : Msg -> State -> (State, Cmd Msg)
> update msg state = case msg of
> UpdateThis -> …
> UpdateThat -> …
>
> My problem is that the state can be either Loading or Displaying, but most
> of the messages only make sense in the Displaying state, leading me to code
> like this:
>
> update : Msg -> State -> (State, Cmd Msg)
> update msg state = case msg of
> UpdateThis -> case state of
> Displaying stuff -> …
> _ -> (Failed "Invalid state", Cmd.none)
> UpdateThat -> case state of
> Displaying stuff -> …
> _ -> (Failed "Invalid state", Cmd.none)
>
> Obviously, this is dumb. How can I “divide” the loading and the displaying
> part of the app? (Assuming that UpdateThis and UpdateThat can only arrive
> in the correct, Displaying state.)
>
> Thank you!
>
> T.
>
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