Here are some real world examples of record updates that could be
streamlined at the language level, including attempts to simplify UI code
defining record updates.
-- Update.elm
update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
case msg of
Update updater ->
( updater model, Cmd.none )
SaveFamily family ->
( model, Cmd.saveFamily family )
_ ->
( model, Cmd.none )
-- View.elm
selected_family : Model -> UI.Node Msg
selected_family model =
UI.form
[ UI.class "fluid"
, UI.onSubmit <| SaveFamily model.family
]
[ UI.input
[ UI.label "Name"
, UI.value model.family.name
, UI.onInput <| \val -> Update <| familyUpdater (\family -> {
family | name = val })
]
]
familyUpdater : (Family -> Family) -> Model -> Model
familyUpdater updater model =
{ model | family = updater model.family }
-- familyUpdater looks simple enough, but at production scale with multiple
embedded records, a few of these functions must be chained together to
complete what could be a simple update such as
model.family.contact.address.street = "Main Street"
-- Multiple specific Msg types such as UpdateFamily can be created to
"clean" the view, but then it becomes really hard to achieve separation of
concern as the Update function grows with out-of-context logic. Those
updater functions are then moved to the Update file or you have to use many
layers of let bindings. There are two concerns here, the update behavior
being defined in the context of the form or becoming overly complex due to
embedded records. The latter is more important.
-- Here's an example from another real world app :
RcvGeocode geocode ->
let
address =
extractAddress geocode
updated =
address |> updateAddress |> updateContact |> updateProfile
|> updateUser model
in
( { updated | geocode = geocode }, Cmd.none )
-- This would look much nicer in my opinion :
RcvGeocode geocode ->
( { model | user.profile.contact.address = extractAddress geocode
}, Cmd.none )
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