Elm example program

Main.elm

import Html exposing (..)
import Html.Attributes exposing (..)
import Html.Events exposing (..)
import Browser exposing (sandbox)

type alias Model =
  { message : String
  , count : Int
  }

type Msg =
    Message String
  | Increment
  | Decrement

initialModel : Model
initialModel =
  Model "Hi, this is state" 0

update : Msg -> Model -> Model
update msg model =
  case msg of
    Message newMessage ->
      { model | message = newMessage }
    Increment ->
      { model | count = model.count + 1 }
    Decrement ->
      { model | count = model.count - 1 }

view : Model -> Html Msg
view model =
  div []
    [ input [ placeholder "Type some stuff", onInput Message ] []
    , div [] [ text model.message ]
    , button [ onClick Increment ] [ text "+" ]
    , button [ onClick Decrement ] [ text "-" ]
    , div [] [ text (String.fromInt model.count) ]
    ]

main : Program () Model Msg
main =
  sandbox
  { init = initialModel
  , view = view
  , update = update
  }