sleep_example.exs

urls = ["http://www.google.com", "http://www.bing.com", "http://www.yahoo.com"]

for_tasks = for {url, i} <- Enum.with_index(urls) do
  Task.async(fn ->
    :timer.sleep(3000 * i)
    IO.puts("for ##{i}: #{url}")
  end)
end

map_tasks = urls
  |> Enum.with_index
  |> Enum.map(fn({url, i}) ->
    Task.async(fn ->
      :timer.sleep(9000 + 3000 * i)
      IO.puts("map ##{i}: #{url}")
    end)
  end)

Task.yield_many(Enum.concat(for_tasks, map_tasks), 20000)