Elm for Real Work

type Model =
  {username : String
  ,password : String
  ,lastError : Maybe Error
  ,credentials : Maybe AuthToken}

type Action
  = Submit
  | ChangeUsername String
  | ChangePassword String
  | LoginResponse (Result Error AuthToken)

update : Action -> Model -> Model
update action model =
  case action of
    ChangeUsername s -> {model | username <- s}
    ChangePassword s -> {model | password <- s}
    ...

submitForm : Model -> Effects (Result Error AuthToken)
submitForm model =
  encodeForm model
  |> post decodeAuthToken "/auth/login"
  |> asEffect

decodeAuthToken : String -> AuthToken
decodeAuthToken = ...

update : Action -> Model -> (Model, Effects Action)
update action model =
  case action of
    ChangeUsername s -> ({model | username <- s}, none)
    ChangePassword s -> ({model | password <- s}, none)
    ...

Submit -> ({model | loading <- True
                  , lastError <- Nothing}
          ,submitForm model.username model.password
           |> Effects.map LoginResponse)

LoginResponse (Ok token)  -> ({loading = False
                              ,lastError = Nothing
                              ,credentials = Just token}
                             ,none)
LoginResponse (Err error) -> ({loading = False
                              ,lastError = Just error
                              ,credentials = None}
                             ,none)

loginForm : Model -> Html
loginForm model =
  form []
       [input [type' "text"
              ,class "form-control"
              ,autofocus True]
              []
       [input [type' "password"
              ,class "form-control"]
              []
       ,button [class "btn btn-primary btn-block"
               ,type' "button"
               ,disabled (model.username == "" ||
                          model.password == "")]
               [text "Log In"]]

loginForm : Address Action -> Model -> Html
loginForm address model =
  form []
       [input [type' "text"
              ,class "form-control"
              ,onChange address Username
              ,autofocus True]
              []
       [input [type' "password"
              ,class "form-control"
              ,onChange address Password]
              []
       ,button [class "btn btn-primary btn-block"
               ,type' "button"
               ,disabled (model.username == "" ||
                          model.password == "")
               ,onClick address Submit]
               [text "Log In"]]

{
    spatialReference: {
        wkid: 4326,
        latestWkid: 4326
    },
    candidates: [
        {
            address: "Royal Festival Hall",
            location: {
                x: -0.11599726799954624,
                y: 51.50532882800047
            },
            score: 100,
            attributes: { },
            extent: {
                xmin: -0.120998,
                ymin: 51.500329,
                xmax: -0.110998,
                ymax: 51.510329
            }
        }
    ]
}

type alias Place =
  {address: String
  ,latitude: Float
  ,longitude: Float}

decodePlaces : Decoder (List Candidate)
decodePlaces = "candidates" := (list decodePlace)

decodePlace : Decoder Place
decodePlace =
  Place `map`   ("address" := string)
        `apply` (at ["location", "x"] float)
        `apply` (at ["location", "y"] float)

type alias AnalyticsEvent =
  {category : String
  ,action : String}

toAnalyticsEvent : Action -> Maybe AnalyticsEvent
toAnalyticsEvent action =
  case action of
    BuyProduct id           -> Just {category = "Buy",   action = "Product"}
    ShareProduct Twitter id -> Just {category = "Share", action = "Twitter"}
    ...
    _                       -> Nothing

toAnalyticsEffect : Action -> Effects Action
toAnalyticsEffect action =
  case toAnalyticsEvent action of
    Nothing -> none
    Just event -> sendEvent AnalyticsSent event

updateWithAnalytics : Action -> Model -> (Model, Effects Action)
updateWithAnalytics action model =
  let (newModel,newFx) = update action model
  in (newModel, batch [newFx, toAnalyticsEffect action])

var sendEvent = F2(function (success, event) {
    return Task.asyncFunction(function(callback) {
        ga('send', 'event', event.category, event.action);

        return callback(Task.succeed(success));
    });
});