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211 lines
8.5 KiB
EmacsLisp
211 lines
8.5 KiB
EmacsLisp
;;; cal-persia.el --- calendar functions for the Persian calendar.
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;; Copyright (C) 1996, 1997 Free Software Foundation, Inc.
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;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
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;; Keywords: calendar
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;; Human-Keywords: Persian calendar, calendar, diary
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software; you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation; either version 2, or (at your option)
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;; any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs; see the file COPYING. If not, write to the
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;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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;; Boston, MA 02111-1307, USA.
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;;; Commentary:
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;; This collection of functions implements the features of calendar.el and
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;; diary.el that deal with the Persian calendar.
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;; Technical details of all the calendrical calculations can be found in
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;; ``Calendrical Calculations'' by Nachum Dershowitz and Edward M. Reingold,
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;; Cambridge University Press (1997).
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;; Comments, corrections, and improvements should be sent to
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;; Edward M. Reingold Department of Computer Science
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;; (217) 333-6733 University of Illinois at Urbana-Champaign
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;; reingold@cs.uiuc.edu 1304 West Springfield Avenue
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;; Urbana, Illinois 61801
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;;; Code:
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(require 'cal-julian)
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(defvar persian-calendar-month-name-array
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["Farvardin" "Ordibehest" "Xordad" "Tir" "Mordad" "Sahrivar" "Mehr" "Aban"
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"Azar" "Dey" "Bahman" "Esfand"])
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(defvar persian-calendar-epoch (calendar-absolute-from-julian '(3 19 622))
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"Absolute date of start of Persian calendar = March 19, 622 A.D. (Julian).")
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(defun persian-calendar-leap-year-p (year)
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"True if YEAR is a leap year on the Persian calendar."
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(< (mod (* (mod (mod (if (<= 0 year)
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; No year zero
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(+ year 2346)
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(+ year 2347))
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2820)
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768)
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683)
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2820)
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683))
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(defun persian-calendar-last-day-of-month (month year)
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"Return last day of MONTH, YEAR on the Persian calendar."
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(cond
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((< month 7) 31)
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((or (< month 12) (persian-calendar-leap-year-p year)) 30)
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(t 29)))
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(defun calendar-absolute-from-persian (date)
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"Compute absolute date from Persian date DATE.
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The absolute date is the number of days elapsed since the (imaginary)
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Gregorian date Sunday, December 31, 1 BC."
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(let ((month (extract-calendar-month date))
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(day (extract-calendar-day date))
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(year (extract-calendar-year date)))
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(if (< year 0)
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(+ (calendar-absolute-from-persian
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(list month day (1+ (mod year 2820))))
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(* 1029983 (floor year 2820)))
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(+ (1- persian-calendar-epoch); Days before epoch
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(* 365 (1- year)) ; Days in prior years.
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(* 683 ; Leap days in prior 2820-year cycles
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(floor (+ year 2345) 2820))
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(* 186 ; Leap days in prior 768 year cycles
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(floor (mod (+ year 2345) 2820) 768))
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(floor; Leap years in current 768 or 516 year cycle
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(* 683 (mod (mod (+ year 2345) 2820) 768))
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2820)
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-568 ; Leap years in Persian years -2345...-1
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(calendar-sum ; Days in prior months this year.
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m 1 (< m month)
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(persian-calendar-last-day-of-month m year))
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day)))) ; Days so far this month.
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(defun calendar-persian-year-from-absolute (date)
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"Persian year corresponding to the absolute DATE."
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(let* ((d0 ; Prior days since start of 2820 cycles
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(- date (calendar-absolute-from-persian (list 1 1 -2345))))
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(n2820 ; Completed 2820-year cycles
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(floor d0 1029983))
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(d1 ; Prior days not in n2820
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(mod d0 1029983))
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(n768 ; 768-year cycles not in n2820
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(floor d1 280506))
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(d2 ; Prior days not in n2820 or n768
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(mod d1 280506))
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(n1 ; Years not in n2820 or n768
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; we want is
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; (floor (+ (* 2820 d2) (* 2820 366)) 1029983))
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; but that causes overflow, so we use
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(let ((a (floor d2 366)); we use 366 as the divisor because
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; (2820*366 mod 1029983) is small
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(b (mod d2 366)))
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(+ 1 a (floor (+ (* 2137 a) (* 2820 b) 2137) 1029983))))
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(year (+ (* 2820 n2820); Complete 2820 year cycles
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(* 768 n768) ; Complete 768 year cycles
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(if ; Remaining years
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; Last day of 2820 year cycle
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(= d1 1029617)
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(1- n1)
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n1)
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-2345))) ; Years before year 1
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(if (< year 1)
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(1- year); No year zero
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year)))
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(defun calendar-persian-from-absolute (date)
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"Compute the Persian equivalent for absolute date DATE.
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The result is a list of the form (MONTH DAY YEAR).
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The absolute date is the number of days elapsed since the imaginary
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Gregorian date Sunday, December 31, 1 BC."
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(let* ((year (calendar-persian-year-from-absolute date))
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(month ; Search forward from Farvardin
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(1+ (calendar-sum m 1
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(> date
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(calendar-absolute-from-persian
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(list
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m
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(persian-calendar-last-day-of-month m year)
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year)))
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1)))
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(day ; Calculate the day by subtraction
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(- date (1- (calendar-absolute-from-persian
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(list month 1 year))))))
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(list month day year)))
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(defun calendar-persian-date-string (&optional date)
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"String of Persian date of Gregorian DATE.
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Defaults to today's date if DATE is not given."
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(let* ((persian-date (calendar-persian-from-absolute
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(calendar-absolute-from-gregorian
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(or date (calendar-current-date)))))
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(y (extract-calendar-year persian-date))
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(m (extract-calendar-month persian-date)))
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(let ((monthname (aref persian-calendar-month-name-array (1- m)))
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(day (int-to-string (extract-calendar-day persian-date)))
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(dayname nil)
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(month (int-to-string m))
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(year (int-to-string y)))
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(mapconcat 'eval calendar-date-display-form ""))))
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(defun calendar-print-persian-date ()
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"Show the Persian calendar equivalent of the selected date."
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(interactive)
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(message "Persian date: %s"
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(calendar-persian-date-string (calendar-cursor-to-date t))))
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(defun calendar-goto-persian-date (date &optional noecho)
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"Move cursor to Persian date DATE.
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Echo Persian date unless NOECHO is t."
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(interactive (persian-prompt-for-date))
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(calendar-goto-date (calendar-gregorian-from-absolute
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(calendar-absolute-from-persian date)))
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(or noecho (calendar-print-persian-date)))
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(defun persian-prompt-for-date ()
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"Ask for a Persian date."
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(let* ((today (calendar-current-date))
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(year (calendar-read
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"Persian calendar year (not 0): "
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'(lambda (x) (/= x 0))
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(int-to-string
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(extract-calendar-year
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(calendar-persian-from-absolute
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(calendar-absolute-from-gregorian today))))))
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(completion-ignore-case t)
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(month (cdr (assoc
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(capitalize
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(completing-read
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"Persian calendar month name: "
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(mapcar 'list
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(append persian-calendar-month-name-array nil))
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nil t))
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(calendar-make-alist persian-calendar-month-name-array
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1 'capitalize))))
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(last (persian-calendar-last-day-of-month month year))
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(day (calendar-read
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(format "Persian calendar day (1-%d): " last)
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'(lambda (x) (and (< 0 x) (<= x last))))))
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(list (list month day year))))
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(defun diary-persian-date ()
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"Persian calendar equivalent of date diary entry."
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(format "Persian date: %s" (calendar-persian-date-string date)))
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(provide 'cal-persia)
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;;; cal-persia.el ends here
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