Counter.elm

import Signal exposing (Signal, Address)
import Html exposing (Html, div, button, text)
import Html.Events exposing (onClick)
import Task

main : Signal Html
main =
  start { model = model
        , view = view
        , update = update }

type alias Model = Int

model : Model
model = 0

view : Address Action -> Model -> Html
view address model =
  div []
    [ button [ onClick address Decrement ] [ text "-" ]
    , div [] [ text (toString model) ]
    , button [ onClick address Increment ] [ text "+" ]
    ]

type Action = Increment
            | Decrement

update : Action -> Model -> Model
update action model =
  case action of
    Increment -> model + 1
    Decrement -> model - 1


-----------------------------------------------------------
-- StartApp
-----------------------------------------------------------
type alias App model action =
    { model : model
    , view : Address action -> model -> Html
    , update : action -> model -> model
    }

start : App Model Action -> Signal Html
start app =
  let
    actions : Signal.Mailbox (Maybe Action)
    actions =
      Signal.mailbox Nothing

    address : Signal.Address Action
    address =
      Signal.forwardTo actions.address Just

    step : Maybe Action -> Model -> Model
    step (Just action) m =
      app.update action m

    model : Signal Model
    model =
      Signal.foldp
        step
        app.model
        actions.signal

  in
    Signal.map (app.view address) model
-----------------------------------------------------------
-- End StartApp
-----------------------------------------------------------