Context in Elm

Here’s the translation of the Go code to Elm, formatted in Markdown suitable for Hugo:

Our example demonstrates how to set up a simple HTTP server in Elm. This server uses the concept of Task and Platform.Sub for handling cancellation and timeouts, which are analogous to the context.Context in other languages. In Elm, we use the elm/http package for HTTP operations and elm/time for time-related functions.

module Main exposing (main)

import Browser
import Html exposing (Html, text)
import Http
import Task exposing (Task)
import Time

type Msg
    = GotResponse (Result Http.Error String)
    | Timeout

type alias Model =
    { result : Maybe String
    }

init : () -> ( Model, Cmd Msg )
init _ =
    ( { result = Nothing }
    , Task.attempt GotResponse (slowRequest "hello")
    )

slowRequest : String -> Task Http.Error String
slowRequest message =
    Task.race
        (Http.task
            { method = "GET"
            , headers = []
            , url = "https://example.com/slow-endpoint"
            , body = Http.emptyBody
            , resolver = Http.stringResolver (\response ->
                case response of
                    Http.GoodStatus_ _ body ->
                        Ok (message ++ "\n" ++ body)
                    _ ->
                        Err (Http.BadBody "Request failed")
            )
            , timeout = Just 10000
            }
        )
        (Task.perform (\_ -> Timeout) (Time.delay 10000 Time.now))

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        GotResponse result ->
            case result of
                Ok value ->
                    ( { model | result = Just value }, Cmd.none )
                Err _ ->
                    ( { model | result = Just "Error occurred" }, Cmd.none )
        Timeout ->
            ( { model | result = Just "Request timed out" }, Cmd.none )

view : Model -> Html Msg
view model =
    text (Maybe.withDefault "Waiting for response..." model.result)

main : Program () Model Msg
main =
    Browser.element
        { init = init
        , update = update
        , subscriptions = \_ -> Sub.none
        , view = view
        }

In this Elm program:

We define a slowRequest function that simulates a slow HTTP request. It uses Task.race to compete between the actual HTTP request and a timeout.
The init function starts the slow request when the application initializes.
The update function handles the response from the server or a timeout, updating the model accordingly.
The view function displays the result of the request or a waiting message.

To run this Elm program, you would typically compile it to JavaScript and include it in an HTML file. Here’s a basic example of how you might set that up:

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Elm HTTP Server Example</title>
</head>
<body>
    <div id="elm"></div>
    <script src="elm.js"></script>
    <script>
        var app = Elm.Main.init({
            node: document.getElementById('elm')
        });
    </script>
</body>
</html>

This example demonstrates how Elm handles asynchronous operations and timeouts in a functional, statically-typed environment. While it doesn’t directly correspond to setting up an HTTP server like in the original example, it shows how you might handle similar concerns in an Elm application.

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Context in Elm