Calendrical.Calendar (Calendrical v2.2.0)

Makes a hand-written calendar: one whose spine, date_to_iso_days/3 and date_from_iso_days/1, the author writes, with leap_year?/1, months_in_year/1 and days_in_month/2, and leap_month/1 where the calendar has a leap month. Every other answer, from the day of the week to the ranges of a quarter, is derived from those and from the facts the options state, as Calendrical.info/0 carries them.

Example

defmodule MyApp.MyCalendar do
  use Calendrical.Calendar,
    epoch: ~D[0001-01-01 Calendar.ISO],
    cldr_calendar_type: :gregorian

  @impl Calendar
  def leap_year?(year), do: rem(year, 4) == 0

  @impl true
  def date_to_iso_days(year, month, day) do
    # ... the calendar's own calculation
  end

  @impl true
  def date_from_iso_days(iso_days) do
    # ... the calendar's own calculation
  end
end

Options

• :epoch (required) is the first day of the calendar's year 1, as a date in a calendar that has already been compiled, such as ~D[0622-03-20 Calendrical.Julian].

• :cldr_calendar_type is the CLDR calendar whose data names the months, days and eras, :gregorian by default.

• :era_calendar_type is the CLDR calendar whose eras the calendar counts years in, the CLDR calendar type by default.

• :months_in_year is the number of months in a year, or {fewest, most} where a leap year has more, as the Hebrew calendar's {12, 13}. The default is 12.

• :weeks is the rule the calendar's own weeks follow: a keyword list with :first_day, 1 for Monday to 7 for Sunday, and :min_days_in_first_week, or :from_first_day for weeks counted from the first day of the year. The default is Monday and 1.

• :year_zero? is whether the calendar has a year 0, true by default; a calendar without one goes from year -1 to year 1.

• :year_cycle is the cycle the years run in, as the sexagenary cycle of 60, or nil.

• :years_in_cycle is the number of years after which the calendar's days and weekdays repeat, where they do, for sampling.

• :location is the place an astronomical calendar is reckoned at, a function of the ISO day number.

• :month_lengths are the lengths a month can have, by month, where the calendar states them rather than having them sampled.

• :parsing_calendar is the calendar a written date is parsed in, the calendar itself by default.

Overriding

The six primitive Calendar callbacks, leap_year?/1, months_in_year/1, days_in_month/2, valid_date?/3, year_of_era/3 and day_of_era/3, and the kernel, leap_month/1, written_date/3, date_from_written_date/3, shift/6 and diff/3, may be defined by the calendar. Every other generated function is a delegation defined before the calendar's own code, so a later definition of one is unreachable: the compiler warns that its clause can never match, and the generated answer stands.