Elm Language The Elm Architecture Program
Example
program is a good pick, when your application does not require any external data for initialization.
It is capable of handling Subscriptions and Commands, which enables way more opportunities for handling I/O, such as HTTP communication or interop with JavaScript.
The initial state is required to return start-up Commands along with the Model.
The initialization of program will require subscriptions to be provided, along with model, view and update.
See the type definition:
program :
{ init : ( model, Cmd msg )
, update : msg -> model -> ( model, Cmd msg )
, subscriptions : model -> Sub msg
, view : model -> Html msg
}
-> Program Never
Example
The simplest way to illustrate, how you can use Subscriptions is to setup a simple Port communication with JavaScript.
See how to build the example in Initialize and build / Embedding into HTML
port module Main exposing (..)
import Html exposing (Html, text)
import Html exposing (program)
main : Program Never
main =
program
{ init = init
, view = view
, update = update
, subscriptions = subscriptions
}
port input : (Int -> msg) -> Sub msg
-- MODEL
type alias Model =
Int
init : ( Model, Cmd msg )
init =
( 0, Cmd.none )
-- UPDATE
type Msg = Incoming Int
update : Msg -> Model -> ( Model, Cmd msg )
update msg model =
case msg of
Incoming x ->
( x, Cmd.none )
-- SUBSCRIPTIONS
subscriptions : Model -> Sub Msg
subscriptions model =
input Incoming
-- VIEW
view : Model -> Html msg
view model =
text (toString model)
<!DOCTYPE html>
<html>
<head>
<script src='elm.js'></script>
</head>
<body>
<div id='app'></div>
<script>var app = Elm.Main.embed(document.getElementById('app'));</script>
<button onclick='app.ports.input.send(1);'>send</button>
</body>
</html>
