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Optional args for holiday-greek-orthodox-easter

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* etc/NEWS: Document this.
* lisp/calendar/holidays.el (holiday-greek-orthodox-easter):
Add optional args N and STRING, mimicking the API and code of
‘holiday-easter-etc’.  From suggestion by Foivos S. Zakkak (Bug#21256).
This commit is contained in:
Paul Eggert 2015-08-13 12:16:25 -07:00
parent 57adf425f5
commit b532875a60
2 changed files with 17 additions and 7 deletions
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3
etc/NEWS
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@ -551,6 +551,9 @@ which means to do nothing special with the mode line in calendars.
The option customizes which day headers receive the
`calendar-weekend-header' face.
---
*** New optional args N and STRING for ‘holiday-greek-orthodox-easter’.
---
*** Many items obsolete since at least version 23.1 have been removed.
The majority were function/variable/face aliases, too numerous to list here.

21
lisp/calendar/holidays.el
View file

@ -791,8 +791,16 @@ is non-nil)."
;; Prior call to calendar-julian-from-absolute will autoload cal-julian.
(declare-function calendar-julian-to-absolute "cal-julian" (date))
(defun holiday-greek-orthodox-easter ()
"Date of Easter according to the rule of the Council of Nicaea."
(defun holiday-greek-orthodox-easter (&optional n string)
"Date of Nth day after Easter (named STRING), if visible in calendar window.
It is calculated according to the rule of the Council of Nicaea.
Negative values of N are interpreted as days before Easter.
STRING is used purely for display purposes. The return value has
the form ((MONTH DAY YEAR) STRING), where the date is that of the
Nth day before or after Easter.
For backwards compatibility, if this function is called with no
arguments, it returns the date of Pascha (Greek Orthodox Easter)."
(let* ((m displayed-month)
(y displayed-year)
(julian-year (progn
@ -808,11 +816,10 @@ is non-nil)."
(paschal-moon ; day after full moon on or after March 21
(- (calendar-julian-to-absolute (list 4 19 julian-year))
shifted-epact))
(nicaean-easter ; Sunday following the Paschal moon
(calendar-gregorian-from-absolute
(calendar-dayname-on-or-before 0 (+ paschal-moon 7)))))
(if (calendar-date-is-visible-p nicaean-easter)
(list (list nicaean-easter "Pascha (Greek Orthodox Easter)")))))
(abs-easter (calendar-dayname-on-or-before 0 (+ paschal-moon 7)))
(greg (calendar-gregorian-from-absolute (+ abs-easter (or n 0)))))
(if (calendar-date-is-visible-p greg)
(list (list greg (or string "Pascha (Greek Orthodox Easter)"))))))
(provide 'holidays)