I am looking for design guidelines on when to model a collection of records
as a Dict vs. a List.
The TodoMVC uses a List, though at first glance a Dict seems like a more
natural match:
- There are several "id based" Msg's (ex. EditingEntry, UpdateEntry,
Delete, Check)
- Using Html.Keyed should be (slightly) easier to use
But I think I understand why a List is more pragmatic.
In (my) practice, things get muddy attempting to implement TodoMVC with a
Dict.
Dict.update wants a (Maybe v -> Maybe v) resulting in nested case
statements which are okay but preferable to avoid.
(...it could be that my FP-fu is too weak to factor a concise expression.
Maybe.map doesn't appear useful as record updates aren't compose-able?)
So, the "mapWhen" idiom (via an "updateEntry" helper) does seem to be the
simplest approach
let
updateEntry t =
if ti.id = id then { t | field = newValue } else t
in
{ model | entries = List.map updateEntry model.entries }
So if Dict isn't the best choice for a use case like TodoMVC...what kinds
of use cases is it good for?
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