Process Mailbox

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Process Mailbox

You’re going to create a Mailbox using a process which loops and receives messages.

mailbox_process = spawn(fn -> Mailbox.loop() end)

You should be able to send the Mailbox a message to add a virtual letter to the mailbox. Print the current list of letters during every loop to prove your spawned process is storing every message in its state.

send(mailbox_process, {:mail, "You've Got Mail!"})
# ["You've Got Mail!"]

send(mailbox_process, {:mail, "You've Got Mail..Again!"})
# ["You've Got Mail..Again!", "You've Got Mail!"]

We won’t typically work directly with processes like this. Instead we’ll rely on abstractions such as GenServer which we will learn about in a future lesson.

Example Solution

defmodule Mailbox do
  def loop(state \\ []) do
    IO.inspect(state)
    receive do
      {:mail, letter} -> loop([letter | state])
    end
  end
end

Implement the Mailbox module below.

defmodule Mailbox do
  @moduledoc """
  Documentation for `Mailbox`
  """

  @doc """
  Recursively loop and receive messages.

  ## Examples

      iex> counter_process = spawn(fn -> Mailbox.loop() end)
      iex> send(counter_process, {:mail, "Hello!"})
  """
  def loop(state \\ []) do
  end
end

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "process_mailbox_reading"
    "exercises" -> "process_mailbox_exercise"
  end

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, save_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(
      progress_path,
      Jason.encode!(Map.put(existing_progress, save_name, completed), pretty: true)
    )
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout -b process-mailbox-exercise
$ git add .
$ git commit -m "finish process mailbox exercise"
$ git push origin process-mailbox-exercise

Create a pull request from your process-mailbox-exercise branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your teacher by including @BrooklinJazz in your PR description to get feedback. You (or your teacher) may merge your PR into your solutions branch after review.

If you are interested in joining the next academy cohort, sign up here to receive more news when it is available.

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