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1 ;;; cal-french.el --- calendar functions for the French Revolutionary calendar.
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2
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3 ;; Copyright (C) 1988, 1989, 1992, 1994 Free Software Foundation, Inc.
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4
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5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
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6 ;; Keywords: calendar
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7 ;; Human-Keywords: French Revolutionary calendar, calendar, diary
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8
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9 ;; This file is part of XEmacs.
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10
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11 ;; XEmacs is free software; you can redistribute it and/or modify it
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12 ;; under the terms of the GNU General Public License as published by
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13 ;; the Free Software Foundation; either version 2, or (at your option)
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14 ;; any later version.
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15
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16 ;; XEmacs is distributed in the hope that it will be useful, but
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17 ;; WITHOUT ANY WARRANTY; without even the implied warranty of
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18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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19 ;; General Public License for more details.
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20
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21 ;; You should have received a copy of the GNU General Public License
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16
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22 ;; along with XEmacs; see the file COPYING. If not, write to the
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23 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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24 ;; Boston, MA 02111-1307, USA.
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0
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25
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26 ;;; Commentary:
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27
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28 ;; This collection of functions implements the features of calendar.el and
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29 ;; diary.el that deal with the French Revolutionary calendar.
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30
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31 ;; Technical details of the French Revolutionary calendar can be found in
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32 ;; ``Calendrical Calculations, Part II: Three Historical Calendars''
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33 ;; by E. M. Reingold, N. Dershowitz, and S. M. Clamen,
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34 ;; Software--Practice and Experience, Volume 23, Number 4 (April, 1993),
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35 ;; pages 383-404.
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36
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37 ;; Comments, corrections, and improvements should be sent to
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38 ;; Edward M. Reingold Department of Computer Science
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39 ;; (217) 333-6733 University of Illinois at Urbana-Champaign
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40 ;; reingold@cs.uiuc.edu 1304 West Springfield Avenue
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41 ;; Urbana, Illinois 61801
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42
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43 ;;; Code:
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44
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45 (require 'calendar)
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46
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47 (defconst french-calendar-month-name-array
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48 ["Vende'miaire" "Brumaire" "Frimaire" "Nivo^se" "Pluvio^se" "Vento^se"
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49 "Germinal" "Flore'al" "Prairial" "Messidor" "Thermidor" "Fructidor"])
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50
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51 (defconst french-calendar-day-name-array
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52 ["Primidi" "Duodi" "Tridi" "Quartidi" "Quintidi" "Sextidi" "Septidi"
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53 "Octidi" "Nonidi" "Decadi"])
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54
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55 (defconst french-calendar-special-days-array
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56 ["de la Vertu" "du Genie" "du Labour" "de la Raison" "de la Recompense"
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57 "de la Revolution"])
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58
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59 (defun french-calendar-leap-year-p (year)
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60 "True if YEAR is a leap year on the French Revolutionary calendar.
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61 For Gregorian years 1793 to 1805, the years of actual operation of the
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62 calendar, uses historical practice based on equinoxes is followed (years 3, 7,
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63 and 11 were leap years; 15 and 20 would have been leap years). For later
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64 years uses the proposed rule of Romme (never adopted)--leap years fall every
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65 four years except century years not divisible 400 and century years that are
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66 multiples of 4000."
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67 (or (memq year '(3 7 11));; Actual practice--based on equinoxes
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68 (memq year '(15 20)) ;; Anticipated practice--based on equinoxes
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69 (and (> year 20) ;; Romme's proposal--never adopted
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70 (zerop (% year 4))
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71 (not (memq (% year 400) '(100 200 300)))
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72 (not (zerop (% year 4000))))))
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73
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74 (defun french-calendar-last-day-of-month (month year)
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75 "Return last day of MONTH, YEAR on the French Revolutionary calendar.
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76 The 13th month is not really a month, but the 5 (6 in leap years) day period of
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77 `sansculottides' at the end of the year."
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78 (if (< month 13)
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79 30
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80 (if (french-calendar-leap-year-p year)
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81 6
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82 5)))
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83
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84 (defun calendar-absolute-from-french (date)
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85 "Compute absolute date from French Revolutionary date DATE.
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86 The absolute date is the number of days elapsed since the (imaginary)
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87 Gregorian date Sunday, December 31, 1 BC."
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88 (let ((month (extract-calendar-month date))
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89 (day (extract-calendar-day date))
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90 (year (extract-calendar-year date)))
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91 (+ (* 365 (1- year));; Days in prior years
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92 ;; Leap days in prior years
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93 (if (< year 20)
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94 (/ year 4);; Actual and anticipated practice (years 3, 7, 11, 15)
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95 ;; Romme's proposed rule (using the Principle of Inclusion/Exclusion)
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96 (+ (/ (1- year) 4);; Luckily, there were 4 leap years before year 20
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97 (- (/ (1- year) 100))
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98 (/ (1- year) 400)
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99 (- (/ (1- year) 4000))))
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100 (* 30 (1- month));; Days in prior months this year
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101 day;; Days so far this month
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102 654414)));; Days before start of calendar (September 22, 1792).
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103
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104 (defun calendar-french-from-absolute (date)
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105 "Compute the French Revolutionary equivalent for absolute date DATE.
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106 The result is a list of the form (MONTH DAY YEAR).
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107 The absolute date is the number of days elapsed since the
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108 \(imaginary) Gregorian date Sunday, December 31, 1 BC."
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109 (if (< date 654415)
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110 (list 0 0 0);; pre-French Revolutionary date
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111 (let* ((approx (/ (- date 654414) 366));; Approximation from below.
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112 (year ;; Search forward from the approximation.
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113 (+ approx
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114 (calendar-sum y approx
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115 (>= date (calendar-absolute-from-french (list 1 1 (1+ y))))
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116 1)))
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117 (month ;; Search forward from Vendemiaire.
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118 (1+ (calendar-sum m 1
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119 (> date
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120 (calendar-absolute-from-french
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121 (list m
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122 (french-calendar-last-day-of-month m year)
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123 year)))
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124 1)))
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125 (day ;; Calculate the day by subtraction.
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126 (- date
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127 (1- (calendar-absolute-from-french (list month 1 year))))))
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128 (list month day year))))
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129
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130 (defun calendar-french-date-string (&optional date)
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131 "String of French Revolutionary date of Gregorian DATE.
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132 Returns the empty string if DATE is pre-French Revolutionary.
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133 Defaults to today's date if DATE is not given."
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134 (let* ((french-date (calendar-french-from-absolute
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135 (calendar-absolute-from-gregorian
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136 (or date (calendar-current-date)))))
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137 (y (extract-calendar-year french-date))
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138 (m (extract-calendar-month french-date))
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139 (d (extract-calendar-day french-date)))
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140 (cond
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141 ((< y 1) "")
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142 ((= m 13) (format "Jour %s de l'Anne'e %d de la Revolution"
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143 (aref french-calendar-special-days-array (1- d))
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144 y))
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145 (t (format "Decade %s, %s de %s de l'Anne'e %d de la Revolution"
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146 (make-string (1+ (/ (1- d) 10)) ?I)
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147 (aref french-calendar-day-name-array (% (1- d) 10))
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148 (aref french-calendar-month-name-array (1- m))
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149 y)))))
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150
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151 (defun calendar-print-french-date ()
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152 "Show the French Revolutionary calendar equivalent of the selected date."
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153 (interactive)
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154 (let ((f (calendar-french-date-string (calendar-cursor-to-date t))))
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155 (if (string-equal f "")
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156 (message "Date is pre-French Revolution")
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157 (message f))))
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158
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159 (defun calendar-goto-french-date (date &optional noecho)
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160 "Move cursor to French Revolutionary date DATE.
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161 Echo French Revolutionary date unless NOECHO is t."
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162 (interactive
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163 (let* ((year (calendar-read
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164 "Anne'e de la Revolution (>0): "
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165 '(lambda (x) (> x 0))
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166 (int-to-string
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167 (extract-calendar-year
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168 (calendar-french-from-absolute
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169 (calendar-absolute-from-gregorian
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170 (calendar-current-date)))))))
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171 (month-list
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172 (mapcar 'list
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173 (append french-calendar-month-name-array
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174 (if (french-calendar-leap-year-p year)
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175 (mapcar
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176 '(lambda (x) (concat "Jour " x))
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177 french-calendar-special-days-array)
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178 (nreverse
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179 (cdr;; we don't want rev. day in a non-leap yr.
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180 (nreverse
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181 (mapcar
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182 '(lambda (x) (concat "Jour " x))
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183 french-calendar-special-days-array))))))))
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184 (completion-ignore-case t)
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185 (month (cdr (assoc
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186 (capitalize
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187 (completing-read
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188 "Mois ou Sansculottide: "
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189 month-list
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190 nil t))
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191 (calendar-make-alist
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192 month-list
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193 1
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194 '(lambda (x) (capitalize (car x)))))))
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195 (decade (if (> month 12)
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196 1
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197 (calendar-read
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198 "De'cade (1-3): "
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199 '(lambda (x) (memq x '(1 2 3))))))
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200 (day (if (> month 12)
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201 (- month 12)
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202 (calendar-read
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203 "Jour (1-10): "
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204 '(lambda (x) (and (<= 1 x) (<= x 10))))))
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205 (month (if (> month 12) 13 month))
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206 (day (+ day (* 10 (1- decade)))))
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207 (list (list month day year))))
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208 (calendar-goto-date (calendar-gregorian-from-absolute
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209 (calendar-absolute-from-french date)))
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210 (or noecho (calendar-print-french-date)))
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211
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212 (defun diary-french-date ()
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213 "French calendar equivalent of date diary entry."
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214 (let ((f (calendar-french-date-string (calendar-cursor-to-date t))))
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215 (if (string-equal f "")
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216 "Date is pre-French Revolution"
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217 f)))
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218
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219 (provide 'cal-french)
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220
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221 ;;; cal-french.el ends here
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