 
   """
   @spec to_erl(t) :: :calendar.datetime
+  def to_erl(naive_datetime)
+
   def to_erl(%{calendar: Calendar.ISO, year: year, month: month, day: day,
                hour: hour, minute: minute, second: second}) do
     {{year, month, day}, {hour, minute, second}}

      2
  """
  @spec day_of_week(Calendar.date) :: non_neg_integer()
  def day_of_week(%{calendar: calendar, year: year, month: month, day: day}) do
    calendar.day_of_week(year, month, day)
  end


  """
  @spec to_erl(Calendar.date) :: :calendar.date
  def to_erl(date)

  def to_erl(%{calendar: Calendar.ISO, year: year, month: month, day: day}) do
    {year, month, day}
  end
