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;;; cal-bahai.el --- calendar functions for the Bahá'í calendar.
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;; Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
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;;   Free Software Foundation, Inc.
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;; Author: John Wiegley <johnw@gnu.org>
;; Keywords: calendar
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;; Human-Keywords: Bahá'í calendar, Bahá'í, Baha'i, Bahai, calendar, diary
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;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation; either version 3, or (at your option)
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;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to the
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;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.
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;;; Commentary:

;; This collection of functions implements the features of calendar.el
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;; and diary.el that deal with the Bahá'í calendar.
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;; The Bahá'í (http://www.bahai.org) calendar system is based on a
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;; solar cycle of 19 months with 19 days each.  The four remaining
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;; "intercalary" days are called the Ayyám-i-Há (days of Há), and are
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;; placed between the 18th and 19th months.  They are meant as a time
;; of festivals preceding the 19th month, which is the month of
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;; fasting.  In Gregorian leap years, there are 5 of these days (Há
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;; has the numerical value of 5 in the arabic abjad, or
;; letter-to-number, reckoning).

;; Each month is named after an attribute of God, as are the 19 days
;; -- which have the same names as the months.  There is also a name
;; for each year in every 19 year cycle.  These cycles are called
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;; Váhids.  A cycle of 19 Váhids (361 years) is called a Kullu-Shay,
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;; which means "all things".

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;; The calendar was named the "Badí` calendar" by its author, the Báb.
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;; It uses a week of seven days, corresponding to the Gregorian week,
;; each of which has its own name, again patterned after the
;; attributes of God.

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;; Note: The days of Ayyám-i-Há are encoded as zero and negative
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;; offsets from the first day of the final month.  So, (19 -3 157) is
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;; the first day of Ayyám-i-Há, in the year 157 BE.
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;;; Code:

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(require 'calendar)
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(defconst calendar-bahai-month-name-array
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  ["Bahá" "Jalál" "Jamál" "`Azamat" "Núr" "Rahmat" "Kalimát" "Kamál"
   "Asmá" "`Izzat" "Mashiyyat" "`Ilm" "Qudrat" "Qawl" "Masá'il"
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   "Sharaf" "Sultán" "Mulk" "`Alá"]
  "Array of the month names in the Bahá'í calendar.")
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(defconst calendar-bahai-epoch (calendar-absolute-from-gregorian '(3 21 1844))
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  "Absolute date of start of Bahá'í calendar = March 21, 1844 AD.")
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(defun calendar-bahai-leap-year-p (year)
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  "True if Bahá'í YEAR is a leap year in the Bahá'í calendar."
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  (calendar-leap-year-p (+ year 1844)))

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(defconst calendar-bahai-leap-base
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  (+ (/ 1844 4) (- (/ 1844 100)) (/ 1844 400))
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  "Number of leap years between 1 and 1844 AD, inclusive.
Used by `calendar-absolute-from-bahai'.")
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(defun calendar-absolute-from-bahai (date)
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  "Compute absolute date from Bahá'í date DATE.
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The absolute date is the number of days elapsed since the (imaginary)
Gregorian date Sunday, December 31, 1 BC."
  (let* ((month (extract-calendar-month date))
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         (day (extract-calendar-day date))
         (year (extract-calendar-year date))
         (prior-years (+ (1- year) 1844))
         (leap-days (- (+ (/ prior-years 4) ; leap days in prior years
                          (- (/ prior-years 100))
                          (/ prior-years 400))
                       calendar-bahai-leap-base)))
    (+ (1- calendar-bahai-epoch)        ; days before epoch
       (* 365 (1- year))                ; days in prior years
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       leap-days
       (calendar-sum m 1 (< m month) 19)
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       (if (= month 19)
           (if (calendar-bahai-leap-year-p year) 5 4)
         0)
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       day)))                           ; days so far this month
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(defun calendar-bahai-from-absolute (date)
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  "Bahá'í date (month day year) corresponding to the absolute DATE."
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  (if (< date calendar-bahai-epoch)
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      (list 0 0 0)                      ; pre-Bahá'í date
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    (let* ((greg (calendar-gregorian-from-absolute date))
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           (gmonth (extract-calendar-month greg))
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           (year (+ (- (extract-calendar-year greg) 1844)
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                    (if (or (> gmonth 3)
                            (and (= gmonth 3)
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                                 (>= (extract-calendar-day greg) 21)))
                        1 0)))
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           (month                       ; search forward from Baha
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            (1+ (calendar-sum m 1
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                  (> date (calendar-absolute-from-bahai (list m 19 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-bahai (list month 1 year))))))
      (list month day year))))

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;;;###cal-autoload
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(defun calendar-bahai-date-string (&optional date)
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  "String of Bahá'í date of Gregorian DATE.
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Defaults to today's date if DATE is not given."
  (let* ((bahai-date (calendar-bahai-from-absolute
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                      (calendar-absolute-from-gregorian
                       (or date (calendar-current-date)))))
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         (y (extract-calendar-year bahai-date))
         (m (extract-calendar-month bahai-date))
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         (d (extract-calendar-day bahai-date))
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         (monthname (if (or (< m 1)     ; pre-Bahai, avoid aref error
                            (and (= m 19)
                                 (<= d 0)))
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                        "Ayyám-i-Há"
                      (aref calendar-bahai-month-name-array (1- m))))
         (day (int-to-string
               (if (<= d 0)
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                   (+ d (if (calendar-bahai-leap-year-p y) 5 4))
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                 d)))
         (year (int-to-string y))
         (month (int-to-string m))
         dayname)
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    (if (< y 1)
        ""
      ;; Can't call calendar-date-string because of monthname oddity.
      (mapconcat 'eval calendar-date-display-form ""))))
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;;;###cal-autoload
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(defun calendar-bahai-print-date ()
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  "Show the Bahá'í calendar equivalent of the selected date."
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  (interactive)
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  (let ((s (calendar-bahai-date-string (calendar-cursor-to-date t))))
   (if (string-equal s "")
       (message "Date is pre-Bahá'í")
     (message "Bahá'í date: %s" s))))
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(define-obsolete-function-alias
  'calendar-print-bahai-date 'calendar-bahai-print-date "23.1")

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(defun calendar-bahai-read-date ()
 "Interactively read the arguments for a Bahá'í date command.
Reads a year, month and day."
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  (let* ((today (calendar-current-date))
         (year (calendar-read
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                "Bahá'í calendar year (not 0): "
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                (lambda (x) (not (zerop x)))
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                (int-to-string
                 (extract-calendar-year
                  (calendar-bahai-from-absolute
                   (calendar-absolute-from-gregorian today))))))
         (completion-ignore-case t)
         (month (cdr (assoc
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                      (completing-read
                       "Bahá'í calendar month name: "
                       (mapcar 'list
                               (append calendar-bahai-month-name-array nil))
                       nil t)
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                      (calendar-make-alist calendar-bahai-month-name-array
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                                           1))))
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         (day (calendar-read "Bahá'í calendar day (1-19): "
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                             (lambda (x) (and (< 0 x) (<= x 19))))))
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    (list (list month day year))))

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(define-obsolete-function-alias
  'calendar-bahai-prompt-for-date 'calendar-bahai-read-date "23.1")

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;;;###cal-autoload
(defun calendar-bahai-goto-date (date &optional noecho)
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  "Move cursor to Bahá'í date DATE; echo Bahá'í date unless NOECHO is non-nil."
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  (interactive (calendar-bahai-read-date))
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  (calendar-goto-date (calendar-gregorian-from-absolute
                       (calendar-absolute-from-bahai date)))
  (or noecho (calendar-bahai-print-date)))

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(define-obsolete-function-alias
  'calendar-goto-bahai-date 'calendar-bahai-goto-date "23.1")

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(defvar displayed-month)
(defvar displayed-year)
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;; FIXME same as islamic.
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;;;###holiday-autoload
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(defun holiday-bahai (month day string)
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  "Holiday on MONTH, DAY (Bahá'í) called STRING.
If MONTH, DAY (Bahá'í) is visible, the value returned is corresponding
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Gregorian date in the form of the list (((month day year) STRING)).  Returns
nil if it is not visible in the current calendar window."
  (let* ((bahai-date (calendar-bahai-from-absolute
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                      (calendar-absolute-from-gregorian
                       (list displayed-month 15 displayed-year))))
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         (m (extract-calendar-month bahai-date))
         (y (extract-calendar-year bahai-date))
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         date)
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    (unless (< m 1)                    ; Bahá'í calendar doesn't apply
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      ;; FIXME makes no sense (?), since there are not 12 months in a year.
      ;; Suspect this was copied from cal-islam.
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      (increment-calendar-month m y (- 10 month))
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      (if (> m 7)                       ; Bahá'í date might be visible
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          (let ((date (calendar-gregorian-from-absolute
                       (calendar-absolute-from-bahai (list month day y)))))
            (if (calendar-date-is-visible-p date)
                (list (list date string))))))))

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(autoload 'diary-list-entries-1 "diary-lib")
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;;;###diary-autoload
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(defun diary-bahai-list-entries ()
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  "Add any Bahá'í date entries from the diary file to `diary-entries-list'.
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Bahá'í date diary entries must be prefaced by `bahai-diary-entry-symbol'
\(normally a `B').  The same diary date forms govern the style of the
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Bahá'í calendar entries, except that the Bahá'í month names cannot be
abbreviated.  The Bahá'í months are numbered from 1 to 19 with Bahá being
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1 and 19 being `Alá.  If a Bahá'í date diary entry begins with
`diary-nonmarking-symbol', the entry will appear in the diary listing, but
will not be marked in the calendar.  This function is provided for use with
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`nongregorian-diary-listing-hook'."
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  (diary-list-entries-1 calendar-bahai-month-name-array
                        bahai-diary-entry-symbol
                        'calendar-bahai-from-absolute))
(define-obsolete-function-alias
  'list-bahai-diary-entries 'diary-bahai-list-entries "23.1")


(autoload 'calendar-mark-1 "diary-lib")
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;;;###diary-autoload
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(defun calendar-bahai-mark-date-pattern (month day year &optional color)
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  "Mark dates in calendar window that conform to Bahá'í date MONTH/DAY/YEAR.
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A value of 0 in any position is a wildcard.  Optional argument COLOR is
passed to `mark-visible-calendar-date' as MARK."
  (calendar-mark-1 month day year 'calendar-bahai-from-absolute
                   'calendar-absolute-from-bahai color))

(define-obsolete-function-alias
  'mark-bahai-calendar-date-pattern 'calendar-bahai-mark-date-pattern "23.1")

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(autoload 'diary-mark-entries-1 "diary-lib")
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;;;###diary-autoload
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(defun diary-bahai-mark-entries ()
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  "Mark days in the calendar window that have Bahá'í date diary entries.
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Marks each entry in `diary-file' (or included files) visible in the calendar
window.  See `diary-bahai-list-entries' for more information."
  (diary-mark-entries-1 calendar-bahai-month-name-array
                        bahai-diary-entry-symbol
                        'calendar-bahai-from-absolute
                        'calendar-bahai-mark-date-pattern))
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(define-obsolete-function-alias
  'mark-bahai-diary-entries 'diary-bahai-mark-entries "23.1")

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(autoload 'diary-insert-entry-1 "diary-lib")

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;;;###cal-autoload
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(defun diary-bahai-insert-entry (arg)
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  "Insert a diary entry.
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For the Bahá'í date corresponding to the date indicated by point.
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Prefix argument ARG makes the entry nonmarking."
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  (interactive "P")
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  (diary-insert-entry-1 nil arg calendar-bahai-month-name-array
                        bahai-diary-entry-symbol
                        'calendar-bahai-from-absolute))
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(define-obsolete-function-alias
  'insert-bahai-diary-entry 'diary-bahai-insert-entry "23.1")

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;;;###cal-autoload
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(defun diary-bahai-insert-monthly-entry (arg)
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  "Insert a monthly diary entry.
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For the day of the Bahá'í month corresponding to the date indicated by point.
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Prefix argument ARG makes the entry nonmarking."
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  (interactive "P")
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  (diary-insert-entry-1 'monthly arg calendar-bahai-month-name-array
                        bahai-diary-entry-symbol
                        'calendar-bahai-from-absolute))
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(define-obsolete-function-alias
  'insert-monthly-bahai-diary-entry 'diary-bahai-insert-monthly-entry "23.1")

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;;;###cal-autoload
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(defun diary-bahai-insert-yearly-entry (arg)
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  "Insert an annual diary entry.
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For the day of the Bahá'í year corresponding to the date indicated by point.
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Prefix argument ARG will make the entry nonmarking."
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  (interactive "P")
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  (diary-insert-entry-1 'yearly arg calendar-bahai-month-name-array
                        bahai-diary-entry-symbol
                        'calendar-bahai-from-absolute))
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(define-obsolete-function-alias
  'insert-yearly-bahai-diary-entry 'diary-bahai-insert-yearly-entry "23.1")

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(defvar date)

;; To be called from list-sexp-diary-entries, where DATE is bound.
;;;###diary-autoload
(defun diary-bahai-date ()
  "Bahá'í calendar equivalent of date diary entry."
  (format "Bahá'í date: %s" (calendar-bahai-date-string date)))


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(provide 'cal-bahai)

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;; Local Variables:
;; coding: utf-8
;; End:

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;; arch-tag: c1cb1d67-862a-4264-a01c-41cb4df01f14
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;;; cal-bahai.el ends here