Demo code from Richard Feldman's https://www.youtube.com/results?search_query=introduction+to+elm

intro_to_elm.elm

import Html exposing (..)
import Html.Attributes exposing (..)
import Html.Events exposing (..)
import Html.App as Html

-- model

type alias Model =
  {
    shelves : Int,
    username : String
  }

model : Model
model =
  { shelves = 2, username = "wendi" }

-- update


type Action =
  Increment Int | Decrement

update : Action -> Model -> Model
update action model =
  case action of
    Increment quantity ->
      { model | shelves = model.shelves + quantity }
    Decrement ->
      { model | shelves = Basics.max 0  (model.shelves - 1) }
    -- _ ->
    --   model

-- view

pluralize : String -> String -> Int -> String
pluralize singular plural quantity =
  if quantity == 1 then
    singular
  else
    plural

shelfButton caption action =
  button [ onClick action ] [ text caption ]

view model =
  let
    isDisabled =
      model.shelves <= 0
    caption =
      (toString model.shelves)
        ++ " "
        ++  (pluralize "shelf" "shelves" model.shelves)
  in
    div
      [ class "content", id "main-body" ]
      [
        h1 [] [ text "Pluralizer"],
        div [] [ shelfButton "Add a shelf" (Increment 10) ],
        div [] [ shelfButton "Explode a shelf" Decrement ],
        text caption
      ]

main =
  Html.beginnerProgram
    { model = model, update = update, view = view }