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239 lines
9.7 KiB
EmacsLisp
239 lines
9.7 KiB
EmacsLisp
;;; cal-coptic.el --- calendar functions for the Coptic/Ethiopic calendars
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;; Copyright (C) 1995, 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: Coptic calendar, Ethiopic 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 Coptic and Ethiopic calendars.
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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 coptic-calendar-month-name-array
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["Tut" "Babah" "Hatur" "Kiyahk" "Tubah" "Amshir" "Baramhat" "Barmundah"
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"Bashans" "Baunah" "Abib" "Misra" "al-Nasi"])
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(defvar coptic-calendar-epoch (calendar-absolute-from-julian '(8 29 284))
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"Absolute date of start of Coptic calendar = August 29, 284 A.D. (Julian).")
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(defvar coptic-name "Coptic")
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(defun coptic-calendar-leap-year-p (year)
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"True if YEAR is a leap year on the Coptic calendar."
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(zerop (mod (1+ year) 4)))
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(defun coptic-calendar-last-day-of-month (month year)
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"Return last day of MONTH, YEAR on the Coptic calendar.
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The 13th month is not really a month, but the 5 (6 in leap years) day period of
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Nisi (Kebus) at the end of the year."
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(if (< month 13)
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30
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(if (coptic-calendar-leap-year-p year)
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6
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5)))
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(defun calendar-absolute-from-coptic (date)
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"Compute absolute date from Coptic 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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(+ (1- coptic-calendar-epoch);; Days before start of calendar
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(* 365 (1- year)) ;; Days in prior years
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(/ year 4) ;; Leap days in prior years
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(* 30 (1- month)) ;; Days in prior months this year
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day))) ;; Days so far this month
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(defun calendar-coptic-from-absolute (date)
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"Compute the Coptic 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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(if (< date coptic-calendar-epoch)
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(list 0 0 0);; pre-Coptic date
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(let* ((approx (/ (- date coptic-calendar-epoch)
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366)) ;; Approximation from below.
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(year ;; Search forward from the approximation.
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(+ approx
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(calendar-sum y approx
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(>= date (calendar-absolute-from-coptic (list 1 1 (1+ y))))
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1)))
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(month ;; Search forward from Tot.
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(1+ (calendar-sum m 1
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(> date
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(calendar-absolute-from-coptic
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(list m
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(coptic-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
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(1- (calendar-absolute-from-coptic (list month 1 year))))))
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(list month day year))))
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(defun calendar-coptic-date-string (&optional date)
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"String of Coptic date of Gregorian DATE.
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Returns the empty string if DATE is pre-Coptic calendar.
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Defaults to today's date if DATE is not given."
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(let* ((coptic-date (calendar-coptic-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 coptic-date))
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(m (extract-calendar-month coptic-date)))
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(if (< y 1)
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""
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(let ((monthname (aref coptic-calendar-month-name-array (1- m)))
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(day (int-to-string (extract-calendar-day coptic-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-coptic-date ()
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"Show the Coptic calendar equivalent of the selected date."
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(interactive)
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(let ((f (calendar-coptic-date-string (calendar-cursor-to-date t))))
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(if (string-equal f "")
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(message "Date is pre-%s calendar" coptic-name)
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(message "%s date: %s" coptic-name f))))
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(defun calendar-goto-coptic-date (date &optional noecho)
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"Move cursor to Coptic date DATE.
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Echo Coptic date unless NOECHO is t."
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(interactive (coptic-prompt-for-date))
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(calendar-goto-date (calendar-gregorian-from-absolute
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(calendar-absolute-from-coptic date)))
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(or noecho (calendar-print-coptic-date)))
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(defun coptic-prompt-for-date ()
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"Ask for a Coptic date."
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(let* ((today (calendar-current-date))
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(year (calendar-read
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(format "%s calendar year (>0): " coptic-name)
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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-coptic-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-string
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(completing-read
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(format "%s calendar month name: " coptic-name)
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(mapcar 'list
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(append coptic-calendar-month-name-array nil))
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nil t)
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(calendar-make-alist coptic-calendar-month-name-array
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1) t)))
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(last (coptic-calendar-last-day-of-month month year))
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(day (calendar-read
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(format "%s calendar day (1-%d): " coptic-name 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-coptic-date ()
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"Coptic calendar equivalent of date diary entry."
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(let ((f (calendar-coptic-date-string date)))
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(if (string-equal f "")
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(format "Date is pre-%s calendar" coptic-name)
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(format "%s date: %s" coptic-name f))))
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(defconst ethiopic-calendar-month-name-array
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["Maskaram" "Teqemt" "Khedar" "Takhsas" "Ter" "Yakatit" "Magabit" "Miyazya"
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"Genbot" "Sane" "Hamle" "Nahas" "Paguem"])
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(defconst ethiopic-calendar-epoch 2796
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"Absolute date of start of Ethiopic calendar = August 29, 8 C.E. (Julian).")
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(defconst ethiopic-name "Ethiopic")
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(defun calendar-absolute-from-ethiopic (date)
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"Compute absolute date from Ethiopic 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 ((coptic-calendar-epoch ethiopic-calendar-epoch))
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(calendar-absolute-from-coptic date)))
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(defun calendar-ethiopic-from-absolute (date)
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"Compute the Ethiopic 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 ((coptic-calendar-epoch ethiopic-calendar-epoch))
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(calendar-coptic-from-absolute date)))
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(defun calendar-ethiopic-date-string (&optional date)
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"String of Ethiopic date of Gregorian DATE.
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Returns the empty string if DATE is pre-Ethiopic calendar.
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Defaults to today's date if DATE is not given."
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(let ((coptic-calendar-epoch ethiopic-calendar-epoch)
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(coptic-name ethiopic-name)
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(coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
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(calendar-coptic-date-string date)))
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(defun calendar-print-ethiopic-date ()
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"Show the Ethiopic calendar equivalent of the selected date."
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(interactive)
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(let ((coptic-calendar-epoch ethiopic-calendar-epoch)
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(coptic-name ethiopic-name)
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(coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
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(call-interactively 'calendar-print-coptic-date)))
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(defun calendar-goto-ethiopic-date (date &optional noecho)
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"Move cursor to Ethiopic date DATE.
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Echo Ethiopic date unless NOECHO is t."
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(interactive
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(let ((coptic-calendar-epoch ethiopic-calendar-epoch)
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(coptic-name ethiopic-name)
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(coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
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(coptic-prompt-for-date)))
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(calendar-goto-date (calendar-gregorian-from-absolute
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(calendar-absolute-from-ethiopic date)))
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(or noecho (calendar-print-ethiopic-date)))
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(defun diary-ethiopic-date ()
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"Ethiopic calendar equivalent of date diary entry."
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(let ((coptic-calendar-epoch ethiopic-calendar-epoch)
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(coptic-name ethiopic-name)
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(coptic-calendar-month-name-array ethiopic-calendar-month-name-array))
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(diary-coptic-date)))
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(provide 'cal-coptic)
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;;; arch-tag: 72d49161-25df-4072-9312-b182cdca7627
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;;; cal-coptic.el ends here
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