Updating deep records in Elm

updating-deep-records.elm

module Main exposing (..)

import Html exposing (..)
import Html.Attributes exposing (..)
import Html.Events exposing (onInput)


main =
    program
        { init = init
        , update = update
        , view = view
        , subscriptions = (always Sub.none)
        }



-- INIT


type alias Model =
    { a :
        { b :
            { c : Int
            }
        }
    }


initialModel =
    { a = { b = { c = 1 } } }


init : ( Model, Cmd Msg )
init =
    ( initialModel, Cmd.none )



-- UPDATE


type Msg
    = UpdateC String


update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        UpdateC val ->
            (updateModel model val) ! [ Cmd.none ]



-- HELPER


updateModel : Model -> String -> Model
updateModel model val =
    let
        levelA =
            model.a

        levelB =
            levelA.b

        intVal =
            Result.withDefault 0 <| String.toInt val
    in
        { model
            | a =
                { levelA
                    | b =
                        { levelB | c = intVal }
                }
        }



-- VIEW


view : Model -> Html Msg
view model =
    div []
        [ input [ value <| toString model.a.b.c, onInput <| UpdateC ] []
        , text <| toString model
        ]