Http Server in Elm

Here’s the translation of the HTTP Server example from Go to Elm, formatted in Markdown suitable for Hugo:

import Html exposing (Html, div, text)
import Http

-- A fundamental concept in Elm HTTP servers is the use of
-- commands and subscriptions. We'll define our main function
-- to initialize our application and handle HTTP requests.

main : Program () Model Msg
main =
    Browser.element
        { init = init
        , update = update
        , subscriptions = subscriptions
        , view = view
        }

-- Model represents the state of our application
type alias Model =
    { response : String
    }

-- Init function sets up the initial state and commands
init : () -> (Model, Cmd Msg)
init _ =
    ( { response = "" }
    , Cmd.none
    )

-- Msg represents the different types of messages our app can receive
type Msg
    = GotHello (Result Http.Error String)
    | GotHeaders (Result Http.Error String)

-- Update function handles the messages and updates the model
update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
    case msg of
        GotHello result ->
            case result of
                Ok response ->
                    ( { model | response = response }, Cmd.none )
                Err _ ->
                    ( { model | response = "Error fetching hello" }, Cmd.none )
        
        GotHeaders result ->
            case result of
                Ok response ->
                    ( { model | response = response }, Cmd.none )
                Err _ ->
                    ( { model | response = "Error fetching headers" }, Cmd.none )

-- Subscriptions function sets up any ongoing subscriptions
subscriptions : Model -> Sub Msg
subscriptions _ =
    Sub.none

-- View function renders the HTML
view : Model -> Html Msg
view model =
    div []
        [ text model.response
        ]

-- Helper functions to make HTTP requests
getHello : Cmd Msg
getHello =
    Http.get
        { url = "http://localhost:8090/hello"
        , expect = Http.expectString GotHello
        }

getHeaders : Cmd Msg
getHeaders =
    Http.get
        { url = "http://localhost:8090/headers"
        , expect = Http.expectString GotHeaders
        }

In Elm, we don’t directly create an HTTP server. Instead, we typically create a client-side application that interacts with a server. This example shows how to create an Elm application that can make requests to an HTTP server.

The main function sets up our Elm application. It uses the Browser.element to create a program that can be embedded in an HTML page.

We define a Model to represent our application’s state, and Msg types to represent different events our application can handle.

The update function handles these messages, updating the model and potentially sending out commands.

The view function renders our application’s HTML based on the current model state.

We’ve also defined two helper functions, getHello and getHeaders, which make HTTP GET requests to the “/hello” and “/headers” endpoints respectively.

To run this Elm application, you would typically compile it to JavaScript and then load it in an HTML page. The compiled JavaScript would then make requests to your HTTP server.

Note that this is a client-side implementation. In a real-world scenario, you’d need a separate server-side component (which could be written in a language like Node.js, Python, or even Go) to actually handle these HTTP requests.

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Http Server in Elm