[elm-discuss] Long form: how to handle model, Msg and update?

[Eduardo Cuducos]

Hi all,

I'm writing an application that has a “advanced search” form. In my context
it means a form with approx. 20 input fields.

As a newbie the only way I could think of coding this is quite repetitive.
I bet that there is a more cleaver and a DRY way to do it, but I couldn't
figure out how. Any ideias?

This is the terrible idea I have in mind:

1. My initial model would have 20 form fields definition like that:

initialModel =
    { form :
        { applicant =
            { label = "Applicant name"
            , selected = True
            , value = ""
            , msg = UpdateApplicant
            }
        , year =
            { label = "Year"
            , selected = True
            , value = ""
            , msg = UpdateYear
            }
        , state =
            { label = "State"
            , selected = True
            , value = ""
            , msg = UpdateState
            }
        …
        }
    …
    }


2. Consequently my type Msg would have another 20 very similar fields:

type Msg
    = UpdateApplicant String
    | UpdateYear String
    | UpdateState
    | …

3. And my update would have 20 very similar cases:

update msg model =
    case msg of
        UpdateApplicant query ->
            let
                applicant =
                    model.form.applicant

                newApplicant =
                    { applicant | value = query }

                currentForm =
                    model.form

                form =
                    { currentForm | applicant = newApplicant }
            in
                ( { model | form = form }, Cmd.none )

        UpdateYear query ->
            let
                year =
                    model.form.year

                newYear =
                    { year | value = query }

                currentForm =
                    model.form

                form =
                    { currentForm | year = newYear }
            in
                ( { model | form = form }, Cmd.none )

        UpdateState query ->
            let
                state =
                    model.form.state

                newState =
                    { state | value = query }

                currentForm =
                    model.form

                form =
                    { currentForm | state = newState }
            in
                ( { model | form = form }, Cmd.none )

Many thanks,

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