Elm 0.17. A simple filtering digits from Keyboard.presses example

elm.package.json

  "version": "1.0.0",
  "summary": "let people do a cool thing in a fun way",
  "repository": "https://github.com/user/project.git",
  "license": "BSD3",
  "source-directories": [
      "."
  ],
  "exposed-modules": [],
  "dependencies": {
    "elm-lang/core": "4.0.0 <= v < 5.0.0",
    "elm-lang/html": "1.0.0 <= v < 2.0.0",
    "elm-lang/keyboard": "1.0.0 <= v < 2.0.0",
  },
  "elm-version": "0.17.0 <= v < 0.18.0"
}

Main.elm

import Html exposing (Html, text, div)
import Html.App as Html
import Keyboard exposing (..)
import Char exposing (..)

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

-- MODEL

type alias Model = Char

init : (Model, Cmd Msg)
init =
  (' ', Cmd.none)

-- UPDATE

type Msg
  = Presses Char

update: Msg -> Model -> (Model, Cmd Msg)
update msg model =
  case msg of
    Presses code ->
      if Char.isDigit code == True
      then
        (code, Cmd.none)
      else
        (model, Cmd.none)

-- SUBSCRIPTIONS

subscriptions: Model -> Sub Msg
subscriptions model =
  Keyboard.presses (\code -> Presses (fromCode code))

-- VIEW

view: Model -> Html Msg
view model =
  let
    str =
      if model == ' '
      then "Press a key"
      else "You pressed: " ++ (toString model)
  in
    Html.text str