Select in Elm

Here’s the translated code and explanation in Elm, formatted in Markdown suitable for Hugo:

Our example demonstrates how to work with multiple asynchronous operations in Elm. We’ll use the Task module to simulate concurrent operations and the Task.sequence function to handle multiple tasks.

import Task exposing (Task)
import Process
import Html exposing (Html, div, text)
import Time

-- Define our main function
main : Program () Model Msg
main =
    Html.program
        { init = init
        , view = view
        , update = update
        , subscriptions = \_ -> Sub.none
        }

-- Model
type alias Model =
    { messages : List String }

init : ( Model, Cmd Msg )
init =
    ( { messages = [] }
    , Task.perform identity (Task.sequence [task1, task2])
    )

-- Update
type Msg
    = GotResults (List String)

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        GotResults results ->
            ( { model | messages = results }, Cmd.none )

-- View
view : Model -> Html Msg
view model =
    div [] (List.map (\msg -> div [] [ text msg ]) model.messages)

-- Tasks
task1 : Task Never String
task1 =
    Process.sleep 1000
        |> Task.andThen (\_ -> Task.succeed "one")

task2 : Task Never String
task2 =
    Process.sleep 2000
        |> Task.andThen (\_ -> Task.succeed "two")

In this example, we create two tasks, task1 and task2, which simulate asynchronous operations that complete after 1 and 2 seconds respectively. We use Task.sequence to run both tasks concurrently and collect their results.

The init function starts both tasks immediately when the program begins. As each task completes, its result is added to the model’s messages list.

The view function simply displays all the messages that have been received.

When you run this program, you’ll see “one” appear after about 1 second, and “two” appear after about 2 seconds. The total execution time will be around 2 seconds since both tasks run concurrently.

This approach in Elm provides a way to handle multiple asynchronous operations, similar to the select statement in other languages. However, Elm’s approach is more functional and fits well with its architecture of model-update-view.