How to model a transient state?

[Jacky See]

Here is a simplified scenario:

type alias Item = { text : String, readState : ReadState, ... }

type ReadState = Read | Unread

type alias Model = { items : List Item }

In the item list view, there is a filter switch: All or Unread.
When the 'Unread' switch is on, it lists all unread items.

Item can be marked as 'Read' by clicking on a item's button,
but then the item immediately disappeared from the filtered list view,
which brings bad user experience.

I'm thinking how should I model such that the just clicked 'unread'
item remains on the filtered list until some other refresh happen?
How to model this 'to be Read' state?

[Mark Hamburg]

If items had identifiers, then I would have some notion of an optional current item in the model or an "except this item" in the filter portion of the model and then have the filter not remove the current item. This can be extended to handle sets of selected items in a natural way. Basically, you want a filter that says "all unread items plus this other item even if it happens to have been read". So, you just need a way to indicate that other item.

Mark

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[Jacky See]

My current approach is to have a `readStateToBe` which contains the pending update state.
and 'flush update' (write `readStateToBe` to `readState`) on appropriate update branch (e.g. switching filter).

[Nick H]

What if you added a third value to the ReadState type?

type ReadState = Read | Unread | Marked

Then your filtered view will show both Unread and Marked. When the user refreshes, you can map all the Marked items to Read.

On Thu, Oct 20, 2016 at 12:43 AM, Jacky See <jack...@gmail.com> wrote:

My current approach is to have a `readStateToBe` which contains the pending update state.
and 'flush update' (write `readStateToBe` to `readState`) on appropriate update branch (e.g. switching filter).

[Jacky]

Thanks! "Marked" is clearer and reflect what's happening on the screen.

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Best Regards,
Jacky See