Main.elm

module Main exposing (..)

import Html exposing (Html, button, div, text)
import Html.Events exposing (onClick)
import Http
import Json.Decode as Decode


main =
    Html.program
        { init = init
        , view = view
        , update = update
        , subscriptions = subscriptions
        }



-- model


type alias Model =
    { value : Int
    , delta : Int
    , netErr : String
    }


init : ( Model, Cmd Msg )
init =
    ( Model 0 1 "", Cmd.none )



-- update


type Msg
    = Inc
    | Dec
    | Update
    | UpdateResult (Result Http.Error String)


update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        Inc ->
            ( { model | value = model.value + model.delta }, Cmd.none )

        Dec ->
            ( { model | value = model.value - model.delta }, Cmd.none )

        Update ->
            ( model, getDeltaUpdate "latest_delta" )

        UpdateResult (Ok newDelta) ->
            case String.toInt newDelta of
                Ok i ->
                    ( { model | delta = i }, Cmd.none )

                Err xi ->
                    ( model, Cmd.none )

        UpdateResult (Err x) ->
            ( model, Cmd.none )


getDeltaUpdate : String -> Cmd Msg
getDeltaUpdate url =
    let
        u = "http://localhost:8080/" ++ url
    in
    Http.send
        UpdateResult
        (Http.get u decodeJSON)


decodeJSON : Decode.Decoder String
decodeJSON =
    Decode.at [ "data", "delta" ] Decode.string



-- view


view : Model -> Html Msg
view model =
    div []
        [ button [ onClick Inc ] [ text "+" ]
        , button [ onClick Dec ] [ text "-" ]
        , div [] [ text (toString model) ]
        , button [ onClick Update ] [ text "update delta" ]
        ]



-- subscriptions


subscriptions : Model -> Sub Msg
subscriptions model =
    Sub.none

notes.txt

Install Forefox add-on CORS-Everywhere and make sure it's icon is green colored

server.py

import time
import bottle

@bottle.route("/latest_delta")
def latest_delta():
    time.sleep(1.5)
    return {'data':{'delta':'4'}}

if __name__ == '__main__':
    bottle.run()