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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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22 ;; along with XEmacs; see the file COPYING. If not, write to the Free
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23 ;; Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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24
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25 ;;; Commentary:
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26
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27 ;; This collection of functions implements the features of calendar.el and
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28 ;; diary.el that deal with the French Revolutionary calendar.
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29
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30 ;; Technical details of the French Revolutionary calendar can be found in
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31 ;; ``Calendrical Calculations, Part II: Three Historical Calendars''
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32 ;; by E. M. Reingold, N. Dershowitz, and S. M. Clamen,
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33 ;; Software--Practice and Experience, Volume 23, Number 4 (April, 1993),
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34 ;; pages 383-404.
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35
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36 ;; Comments, corrections, and improvements should be sent to
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37 ;; Edward M. Reingold Department of Computer Science
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38 ;; (217) 333-6733 University of Illinois at Urbana-Champaign
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39 ;; reingold@cs.uiuc.edu 1304 West Springfield Avenue
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40 ;; Urbana, Illinois 61801
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41
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42 ;;; Code:
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43
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44 (require 'calendar)
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45
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46 (defconst french-calendar-month-name-array
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47 ["Vende'miaire" "Brumaire" "Frimaire" "Nivo^se" "Pluvio^se" "Vento^se"
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48 "Germinal" "Flore'al" "Prairial" "Messidor" "Thermidor" "Fructidor"])
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49
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50 (defconst french-calendar-day-name-array
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51 ["Primidi" "Duodi" "Tridi" "Quartidi" "Quintidi" "Sextidi" "Septidi"
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52 "Octidi" "Nonidi" "Decadi"])
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53
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54 (defconst french-calendar-special-days-array
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55 ["de la Vertu" "du Genie" "du Labour" "de la Raison" "de la Recompense"
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56 "de la Revolution"])
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57
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58 (defun french-calendar-leap-year-p (year)
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59 "True if YEAR is a leap year on the French Revolutionary calendar.
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60 For Gregorian years 1793 to 1805, the years of actual operation of the
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61 calendar, uses historical practice based on equinoxes is followed (years 3, 7,
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62 and 11 were leap years; 15 and 20 would have been leap years). For later
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63 years uses the proposed rule of Romme (never adopted)--leap years fall every
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64 four years except century years not divisible 400 and century years that are
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65 multiples of 4000."
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66 (or (memq year '(3 7 11));; Actual practice--based on equinoxes
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67 (memq year '(15 20)) ;; Anticipated practice--based on equinoxes
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68 (and (> year 20) ;; Romme's proposal--never adopted
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69 (zerop (% year 4))
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70 (not (memq (% year 400) '(100 200 300)))
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71 (not (zerop (% year 4000))))))
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72
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73 (defun french-calendar-last-day-of-month (month year)
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74 "Return last day of MONTH, YEAR on the French Revolutionary calendar.
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75 The 13th month is not really a month, but the 5 (6 in leap years) day period of
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76 `sansculottides' at the end of the year."
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77 (if (< month 13)
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78 30
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79 (if (french-calendar-leap-year-p year)
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80 6
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81 5)))
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82
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83 (defun calendar-absolute-from-french (date)
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84 "Compute absolute date from French Revolutionary date DATE.
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85 The absolute date is the number of days elapsed since the (imaginary)
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86 Gregorian date Sunday, December 31, 1 BC."
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87 (let ((month (extract-calendar-month date))
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88 (day (extract-calendar-day date))
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89 (year (extract-calendar-year date)))
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90 (+ (* 365 (1- year));; Days in prior years
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91 ;; Leap days in prior years
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92 (if (< year 20)
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93 (/ year 4);; Actual and anticipated practice (years 3, 7, 11, 15)
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94 ;; Romme's proposed rule (using the Principle of Inclusion/Exclusion)
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95 (+ (/ (1- year) 4);; Luckily, there were 4 leap years before year 20
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96 (- (/ (1- year) 100))
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97 (/ (1- year) 400)
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98 (- (/ (1- year) 4000))))
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99 (* 30 (1- month));; Days in prior months this year
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100 day;; Days so far this month
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101 654414)));; Days before start of calendar (September 22, 1792).
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102
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103 (defun calendar-french-from-absolute (date)
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104 "Compute the French Revolutionary equivalent for absolute date DATE.
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105 The result is a list of the form (MONTH DAY YEAR).
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106 The absolute date is the number of days elapsed since the
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107 \(imaginary) Gregorian date Sunday, December 31, 1 BC."
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108 (if (< date 654415)
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109 (list 0 0 0);; pre-French Revolutionary date
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110 (let* ((approx (/ (- date 654414) 366));; Approximation from below.
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111 (year ;; Search forward from the approximation.
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112 (+ approx
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113 (calendar-sum y approx
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114 (>= date (calendar-absolute-from-french (list 1 1 (1+ y))))
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115 1)))
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116 (month ;; Search forward from Vendemiaire.
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117 (1+ (calendar-sum m 1
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118 (> date
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119 (calendar-absolute-from-french
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120 (list m
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121 (french-calendar-last-day-of-month m year)
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122 year)))
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123 1)))
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124 (day ;; Calculate the day by subtraction.
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125 (- date
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126 (1- (calendar-absolute-from-french (list month 1 year))))))
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127 (list month day year))))
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128
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129 (defun calendar-french-date-string (&optional date)
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130 "String of French Revolutionary date of Gregorian DATE.
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131 Returns the empty string if DATE is pre-French Revolutionary.
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132 Defaults to today's date if DATE is not given."
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133 (let* ((french-date (calendar-french-from-absolute
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134 (calendar-absolute-from-gregorian
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135 (or date (calendar-current-date)))))
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136 (y (extract-calendar-year french-date))
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137 (m (extract-calendar-month french-date))
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138 (d (extract-calendar-day french-date)))
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139 (cond
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140 ((< y 1) "")
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141 ((= m 13) (format "Jour %s de l'Anne'e %d de la Revolution"
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142 (aref french-calendar-special-days-array (1- d))
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143 y))
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144 (t (format "Decade %s, %s de %s de l'Anne'e %d de la Revolution"
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145 (make-string (1+ (/ (1- d) 10)) ?I)
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146 (aref french-calendar-day-name-array (% (1- d) 10))
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147 (aref french-calendar-month-name-array (1- m))
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148 y)))))
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149
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150 (defun calendar-print-french-date ()
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151 "Show the French Revolutionary calendar equivalent of the selected date."
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152 (interactive)
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153 (let ((f (calendar-french-date-string (calendar-cursor-to-date t))))
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154 (if (string-equal f "")
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155 (message "Date is pre-French Revolution")
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156 (message f))))
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157
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158 (defun calendar-goto-french-date (date &optional noecho)
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159 "Move cursor to French Revolutionary date DATE.
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160 Echo French Revolutionary date unless NOECHO is t."
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161 (interactive
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162 (let* ((year (calendar-read
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163 "Anne'e de la Revolution (>0): "
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164 '(lambda (x) (> x 0))
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165 (int-to-string
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166 (extract-calendar-year
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167 (calendar-french-from-absolute
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168 (calendar-absolute-from-gregorian
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169 (calendar-current-date)))))))
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170 (month-list
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171 (mapcar 'list
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172 (append french-calendar-month-name-array
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173 (if (french-calendar-leap-year-p year)
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174 (mapcar
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175 '(lambda (x) (concat "Jour " x))
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176 french-calendar-special-days-array)
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177 (nreverse
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178 (cdr;; we don't want rev. day in a non-leap yr.
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179 (nreverse
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180 (mapcar
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181 '(lambda (x) (concat "Jour " x))
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182 french-calendar-special-days-array))))))))
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183 (completion-ignore-case t)
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184 (month (cdr (assoc
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185 (capitalize
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186 (completing-read
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187 "Mois ou Sansculottide: "
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188 month-list
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189 nil t))
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190 (calendar-make-alist
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191 month-list
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192 1
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193 '(lambda (x) (capitalize (car x)))))))
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194 (decade (if (> month 12)
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195 1
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196 (calendar-read
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197 "De'cade (1-3): "
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198 '(lambda (x) (memq x '(1 2 3))))))
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199 (day (if (> month 12)
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200 (- month 12)
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201 (calendar-read
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202 "Jour (1-10): "
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203 '(lambda (x) (and (<= 1 x) (<= x 10))))))
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204 (month (if (> month 12) 13 month))
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205 (day (+ day (* 10 (1- decade)))))
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206 (list (list month day year))))
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207 (calendar-goto-date (calendar-gregorian-from-absolute
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208 (calendar-absolute-from-french date)))
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209 (or noecho (calendar-print-french-date)))
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210
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211 (defun diary-french-date ()
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212 "French calendar equivalent of date diary entry."
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213 (let ((f (calendar-french-date-string (calendar-cursor-to-date t))))
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214 (if (string-equal f "")
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215 "Date is pre-French Revolution"
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216 f)))
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217
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218 (provide 'cal-french)
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219
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220 ;;; cal-french.el ends here
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