todo.exs

main = fn ->
  cmd = IO.gets("Enter a command: ") |> String.trim()

  case cmd do
    "1" ->
      todos = Process.get(:todos) || []
      IO.puts(Enum.join(todos, "\n"))

    "2" ->
      todos = Process.get(:todos) || []
      new_todo = IO.gets("Enter a todo: ") |> String.trim()
      Process.put(:todos, [new_todo | todos])

    x when x in ~w(3 4) ->
      # cheating
      todos = Process.get(:todos) || []
      action = if x == "3", do: "complete", else: "delete"
      idx = IO.gets("Enter a todo to #{action}: ") |> String.trim()
      {idx, _} = Integer.parse(idx)
      new_todos = List.delete_at(todos, idx)
      Process.put(:todos, new_todos)

    "5" ->
      Process.exit(self(), :kill)

    _ ->
      IO.puts("Invalid command")
  end
end

Stream.repeatedly(fn -> main.() end) |> Stream.run()