MS-Windows part of 2011-02-21T23:22:34Z!eggert@cs.ucla.edu, addition of min-max.h.

[emacs.git] / doc / emacs / cal-xtra.texi

@c This is part of the Emacs manual.
@c Copyright (C) 2004-2011  Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@c
@c This file is included either in emacs-xtra.texi (when producing the
@c printed version) or in the main Emacs manual (for the on-line version).

@c Moved here from the Emacs Lisp Reference Manual, 2005-03-26.
@node Advanced Calendar/Diary Usage
@section Customizing the Calendar and Diary

  There are many customizations that you can use to make the calendar and
diary suit your personal tastes.

@menu
* Calendar Customizing::   Calendar layout and hooks.
* Holiday Customizing::    Defining your own holidays.
* Date Display Format::    Changing the format.
* Time Display Format::    Changing the format.
* Diary Customizing::      Defaults you can set.
* Non-Gregorian Diary::    Diary entries based on other calendars.
* Diary Display::          A choice of ways to display the diary.
* Fancy Diary Display::    Sorting diary entries, using included diary files.
* Sexp Diary Entries::     More flexible diary entries.
@end menu

@node Calendar Customizing
@subsection Customizing the Calendar

@vindex calendar-intermonth-text
@cindex calendar layout
@cindex calendar week numbers
  The calendar display unfortunately cannot be changed from three
months, but you can customize the whitespace used by setting the
variables: @code{calendar-left-margin},
@code{calendar-day-header-width}, @code{calendar-day-digit-width},
@code{calendar-column-width}, and @code{calendar-intermonth-spacing}.
To display text @emph{between} the months, for example week numbers,
customize the variables @code{calendar-intermonth-header} and
@code{calendar-intermonth-text} as described in their documentation.

@vindex calendar-holiday-marker
@vindex diary-entry-marker
@vindex calenday-today-marker
  The variable @code{calendar-holiday-marker} specifies how to mark a
date as being a holiday.  Its value may be a single-character string to
insert next to the date, or a face name to use for displaying the date.
Likewise, the variable @code{diary-entry-marker} specifies how to mark a
date that has diary entries, and @code{calenday-today-marker} is used by
the function @code{calendar-mark-today} to mark today's date.  By
default, the calendar uses faces named @code{holiday}, @code{diary}, and
@code{calendar-today} for these purposes.

@vindex calendar-load-hook
  The variable @code{calendar-load-hook} is a normal hook run when the
calendar package is first loaded (before actually starting to display
the calendar).

@vindex calendar-initial-window-hook
  Starting the calendar runs the normal hook
@code{calendar-initial-window-hook}.  Recomputation of the calendar
display does not run this hook.  But if you leave the calendar with the
@kbd{q} command and reenter it, the hook runs again.@refill

@vindex calendar-today-visible-hook
@findex calendar-star-date
  The variable @code{calendar-today-visible-hook} is a normal hook run
after the calendar buffer has been prepared with the calendar when the
current date is visible in the window.  One use of this hook is to
mark today's date; to do that use either of the functions
@code{calendar-mark-today} or @code{calendar-star-date}:

@findex calendar-mark-today
@smallexample
(add-hook 'calendar-today-visible-hook 'calendar-mark-today)
@end smallexample

@vindex calendar-today-invisible-hook
@noindent
  A similar normal hook, @code{calendar-today-invisible-hook} is run if
the current date is @emph{not} visible in the window.

@vindex calendar-move-hook
  Each of the calendar cursor motion commands runs the hook
@code{calendar-move-hook} after it moves the cursor.

@node Holiday Customizing
@subsection Customizing the Holidays

@vindex calendar-holidays
@vindex holiday-oriental-holidays
@vindex holiday-solar-holidays
  Emacs knows about holidays defined by entries on one of several lists.
The lists of holidays that Emacs uses are for
general holidays (@code{holiday-general-holidays}),
local holidays (@code{holiday-local-holidays}),
sun- and moon-related holidays (@code{holiday-solar-holidays}),
Baha'i holidays (@code{holiday-bahai-holidays}),
Christian holidays (@code{holiday-christian-holidays}),
Hebrew (Jewish) holidays (@code{holiday-hebrew-holidays}),
Islamic (Muslim) holidays (@code{holiday-islamic-holidays}),
Oriental holidays (@code{holiday-oriental-holidays}),
and other holidays (@code{holiday-other-holidays}).

You can customize these lists of holidays to your own needs, deleting or
adding holidays as described below.  Set any of them to @code{nil} to
eliminate the associated holidays.

@vindex holiday-general-holidays
  The general holidays are, by default, holidays common throughout the
United States.

@vindex holiday-local-holidays
  There are no default local holidays, but your site may supply some.

@vindex holiday-bahai-holidays
@vindex holiday-christian-holidays
@vindex holiday-hebrew-holidays
@vindex holiday-islamic-holidays
@vindex calendar-bahai-all-holidays-flag
@vindex calendar-christian-all-holidays-flag
@vindex calendar-hebrew-all-holidays-flag
@vindex calendar-islamic-all-holidays-flag
  By default, Emacs does not include all the holidays of the religions
that it knows, only those commonly found in secular calendars.  For a
more extensive collection of religious holidays, you can set any (or
all) of the variables @code{calendar-bahai-all-holidays-flag},
@code{calendar-christian-all-holidays-flag},
@code{calendar-hebrew-all-holidays-flag}, or
@code{calendar-islamic-all-holidays-flag} to @code{t}.

@vindex holiday-other-holidays
  You can set the variable @code{holiday-other-holidays} to any list of
holidays.  This list, normally empty, is intended for individual use.

@cindex holiday forms
  Each of the holiday variables is a list of @dfn{holiday forms}, each
form describing a holiday (or sometimes a list of holidays).

  Here is a table of the possible kinds of holiday form.  Day numbers
and month numbers count starting from 1, but ``dayname'' numbers
count Sunday as 0.  The element @var{string} is always the
description of the holiday, as a string.

@table @code
@item (holiday-fixed @var{month} @var{day} @var{string})
A fixed date on the Gregorian calendar.

@item (holiday-float @var{month} @var{dayname} @var{k} @var{string}
      &optional @var{day})
The @var{k}th @var{dayname} (@var{dayname}=0 for Sunday, and so on)
after or before Gregorian date @var{month}, @var{day}.  Negative @var{k}
means count back from the end of the month.  Optional @var{day} defaults
to 1 if @var{k} is positive, and the last day of @var{month} otherwise.

@item (holiday-chinese @var{month} @var{day} @var{string})
A fixed date on the Chinese calendar.

@item (holiday-hebrew @var{month} @var{day} @var{string})
A fixed date on the Hebrew calendar.

@item (holiday-islamic @var{month} @var{day} @var{string})
A fixed date on the Islamic calendar.

@item (holiday-julian @var{month} @var{day} @var{string})
A fixed date on the Julian calendar.

@item (holiday-sexp @var{sexp} @var{string})
A date calculated by the Lisp expression @var{sexp}.  The expression
should use the variable @code{year} to compute and return the date of a
holiday in the form of a list @code{(@var{month} @var{day} @var{year})},
or @code{nil} if the holiday doesn't happen this year.

@item (if @var{condition} @var{holiday-form})
A holiday that happens only if @var{condition} is true.

@item (@var{function} @r{[}@var{args}@r{]})
A list of dates calculated by the function @var{function}, called with
arguments @var{args}.
@end table

  For example, suppose you want to add Bastille Day, celebrated in
France on July 14 (i.e., the fourteenth day of the seventh month).  You
can do this as follows:

@smallexample
(setq holiday-other-holidays '((holiday-fixed 7 14 "Bastille Day")))
@end smallexample

  Many holidays occur on a specific day of the week, at a specific time
of month.  Here is a holiday form describing Hurricane Supplication Day,
celebrated in the Virgin Islands on the fourth Monday in August:

@smallexample
(holiday-float 8 1 4 "Hurricane Supplication Day")
@end smallexample

@noindent
Here the 8 specifies August, the 1 specifies Monday (Sunday is 0,
Tuesday is 2, and so on), and the 4 specifies the fourth occurrence in
the month (1 specifies the first occurrence, 2 the second occurrence,
@minus{}1 the last occurrence, @minus{}2 the second-to-last occurrence, and
so on).

  You can specify holidays that occur on fixed days of the Baha'i,
Chinese, Hebrew, Islamic, and Julian calendars too.  For example,

@smallexample
(setq holiday-other-holidays
      '((holiday-hebrew 10 2 "Last day of Hanukkah")
        (holiday-islamic 3 12 "Mohammed's Birthday")
        (holiday-julian 4 2 "Jefferson's Birthday")))
@end smallexample

@noindent
adds the last day of Hanukkah (since the Hebrew months are numbered with
1 starting from Nisan), the Islamic feast celebrating Mohammed's
birthday (since the Islamic months are numbered from 1 starting with
Muharram), and Thomas Jefferson's birthday, which is 2 April 1743 on the
Julian calendar.

  To include a holiday conditionally, use either Emacs Lisp's @code{if}
or the @code{holiday-sexp} form.  For example, American presidential
elections occur on the first Tuesday after the first Monday in November
of years divisible by 4:

@smallexample
(holiday-sexp '(if (zerop (% year 4))
                   (calendar-gregorian-from-absolute
                    (1+ (calendar-dayname-on-or-before
                          1 (+ 6 (calendar-absolute-from-gregorian
                                  (list 11 1 year)))))))
              "US Presidential Election")
@end smallexample

@noindent
or

@smallexample
(if (zerop (% displayed-year 4))
    (holiday-fixed 11
           (calendar-extract-day
             (calendar-gregorian-from-absolute
               (1+ (calendar-dayname-on-or-before
                     1 (+ 6 (calendar-absolute-from-gregorian
                              (list 11 1 displayed-year)))))))
           "US Presidential Election"))
@end smallexample

  Some holidays just don't fit into any of these forms because special
calculations are involved in their determination.  In such cases you
must write a Lisp function to do the calculation.  To include eclipses,
for example, add @code{(eclipses)} to @code{holiday-other-holidays}
and write an Emacs Lisp function @code{eclipses} that returns a
(possibly empty) list of the relevant Gregorian dates among the range
visible in the calendar window, with descriptive strings, like this:

@smallexample
(((6 27 1991) "Lunar Eclipse") ((7 11 1991) "Solar Eclipse") ... )
@end smallexample

@node Date Display Format
@subsection Date Display Format
@vindex calendar-date-display-form

  You can customize the manner of displaying dates in the diary, in mode
lines, and in messages by setting @code{calendar-date-display-form}.
This variable holds a list of expressions that can involve the variables
@code{month}, @code{day}, and @code{year}, which are all numbers in
string form, and @code{monthname} and @code{dayname}, which are both
alphabetic strings.  In the American style, the default value of this
list is as follows:

@smallexample
((if dayname (concat dayname ", ")) monthname " " day ", " year)
@end smallexample

@noindent
while in the European style this value is the default:

@smallexample
((if dayname (concat dayname ", ")) day " " monthname " " year)
@end smallexample

@noindent
The default ISO date representation is:

@smallexample
((format "%s-%.2d-%.2d" year (string-to-number month)
         (string-to-number day)))
@end smallexample

@noindent
This specifies a typical American format:

@smallexample
(month "/" day "/" (substring year -2))
@end smallexample

@node Time Display Format
@subsection Time Display Format
@vindex calendar-time-display-form

  The calendar and diary by default display times of day in the
conventional American style with the hours from 1 through 12, minutes,
and either @samp{am} or @samp{pm}.  If you prefer the European style,
also known in the US as military, in which the hours go from 00 to 23,
you can alter the variable @code{calendar-time-display-form}.  This
variable is a list of expressions that can involve the variables
@code{12-hours}, @code{24-hours}, and @code{minutes}, which are all
numbers in string form, and @code{am-pm} and @code{time-zone}, which are
both alphabetic strings.  The default value is:

@smallexample
(12-hours ":" minutes am-pm
          (if time-zone " (") time-zone (if time-zone ")"))
@end smallexample

@noindent
Here is a value that provides European style times:

@smallexample
(24-hours ":" minutes
          (if time-zone " (") time-zone (if time-zone ")"))
@end smallexample

Note that few calendar functions return a time of day (at present, only
solar functions).

@node Diary Customizing
@subsection Customizing the Diary

@vindex diary-show-holidays-flag
  Ordinarily, the diary window indicates any holidays that fall on the
date of the diary entries, either in the mode line or the buffer itself.
The process of checking for holidays can be slow, depending on the
defined holidays.  In that case, setting @code{diary-show-holidays-flag}
to @code{nil} will speed up the diary display.

@vindex diary-number-of-entries
  The variable @code{diary-number-of-entries} controls the number of
days of diary entries to be displayed at one time.  It affects the
initial display when @code{calendar-view-diary-initially-flag} is
@code{t}, as well as the command @kbd{M-x diary}.  For example, a value
of 1 (the default) displays only the current day's diary entries,
whereas a value of 2 will also show the next day's entries.  The value
can also be a vector of seven integers: for example, if the value is
@code{[0 2 2 2 2 4 1]} then no diary entries appear on Sunday, the
current date's and the next day's diary entries appear Monday through
Thursday, Friday through Monday's entries appear on Friday, while on
Saturday only that day's entries appear.

@vindex diary-date-forms
  You can customize the form of dates in your diary file by setting the
variable @code{diary-date-forms}.  This variable is a list of patterns
for recognizing a date.  Each date pattern is a list whose elements may
be regular expressions (@pxref{Regular Expressions,,, elisp, the Emacs
Lisp Reference Manual}) or the symbols @code{month}, @code{day},
@code{year}, @code{monthname}, and @code{dayname}.  All these elements
serve as patterns that match certain kinds of text in the diary file.
In order for the date pattern, as a whole, to match, all of its elements
must match consecutively.

  A regular expression in a date pattern matches in its usual fashion,
using the standard syntax table altered so that @samp{*} is a word
constituent.

  The symbols @code{month}, @code{day}, @code{year}, @code{monthname},
and @code{dayname} match the month number, day number, year number,
month name, and day name of the date being considered.  The symbols that
match numbers allow leading zeros; those that match names allow
capitalization and abbreviation (as specified by
@code{calendar-month-abbrev-array} and
@code{calendar-day-abbrev-array}).  All the symbols can match @samp{*};
since @samp{*} in a diary entry means ``any day'', ``any month'', and so
on, it should match regardless of the date being considered.

  The default value of @code{diary-date-forms} in the American style is
provided by @code{diary-american-date-forms}:

@example
((month "/" day "[^/0-9]")
 (month "/" day "/" year "[^0-9]")
 (monthname " *" day "[^,0-9]")
 (monthname " *" day ", *" year "[^0-9]")
 (dayname "\\W"))
@end example

@noindent
Other default styles are provided by @code{diary-european-date-forms}
and @code{diary-iso-date-forms}.

  The date patterns in the list must be @emph{mutually exclusive} and
must not match any portion of the diary entry itself, just the date and
one character of whitespace.  If, to be mutually exclusive, the pattern
must match a portion of the diary entry text---beyond the whitespace
that ends the date---then the first element of the date pattern
@emph{must} be @code{backup}.  This causes the date recognizer to back
up to the beginning of the current word of the diary entry, after
finishing the match.  Even if you use @code{backup}, the date pattern
must absolutely not match more than a portion of the first word of the
diary entry.  For example, the default value of
@code{diary-european-date-forms} is:

@example
((day "/" month "[^/0-9]")
 (day "/" month "/" year "[^0-9]")
 (backup day " *" monthname "\\W+\\<\\([^*0-9]\\|\\([0-9]+[:aApP]\\)\\)")
 (day " *" monthname " *" year "[^0-9]")
 (dayname "\\W"))
@end example

@noindent
Notice the use of @code{backup} in the third pattern, because it needs
to match part of a word beyond the date itself to distinguish it from
the fourth pattern.

@node Non-Gregorian Diary
@subsection Diary Entries Using non-Gregorian Calendars

  As well as entries based on the standard Gregorian calendar, your
diary can have entries based on Baha'i, Hebrew, or Islamic dates.
Recognition of such entries can be time-consuming, however, and since
most people don't use them, you must explicitly enable their use.  If
you want the diary to recognize Hebrew-date diary entries, for example,
you must do this:

@vindex diary-nongregorian-listing-hook
@vindex diary-nongregorian-marking-hook
@findex diary-hebrew-list-entries
@findex diary-hebrew-mark-entries
@findex diary-islamic-list-entries
@findex diary-islamic-mark-entries
@findex diary-bahai-list-entries
@findex diary-bahai-mark-entries
@smallexample
(add-hook 'diary-nongregorian-listing-hook 'diary-hebrew-list-entries)
(add-hook 'diary-nongregorian-marking-hook 'diary-hebrew-mark-entries)
@end smallexample

@noindent
Similarly, for Islamic and Baha'i entries, add
@code{diary-islamic-list-entries} and @code{diary-islamic-mark-entries}, or
@code{diary-bahai-list-entries} and @code{diary-bahai-mark-entries}.

@vindex diary-bahai-entry-symbol
@vindex diary-hebrew-entry-symbol
@vindex diary-islamic-entry-symbol
  These diary entries have the same formats as Gregorian-date diary
entries; except that @code{diary-bahai-entry-symbol} (default @samp{B})
must precede a Baha'i date, @code{diary-hebrew-entry-symbol} (default
@samp{H}) a Hebrew date, and @code{diary-islamic-entry-symbol} (default
@samp{I}) an Islamic date.  Moreover, non-Gregorian month names may not
be abbreviated (because the first three letters are often not unique).
(Note also that you must use ``Adar I'' if you want Adar of a common
Hebrew year.)  For example, a diary entry for the Hebrew date Heshvan 25
could look like this:

@smallexample
HHeshvan 25 Happy Hebrew birthday!
@end smallexample

@noindent
and would appear in the diary for any date that corresponds to Heshvan 25
on the Hebrew calendar.  And here is an Islamic-date diary entry that matches
Dhu al-Qada 25:

@smallexample
IDhu al-Qada 25 Happy Islamic birthday!
@end smallexample

  As with Gregorian-date diary entries, non-Gregorian entries are
nonmarking if preceded by @code{diary-nonmarking-symbol} (default
@samp{&}).

  Here is a table of commands used in the calendar to create diary
entries that match the selected date and other dates that are similar in
the Baha'i, Hebrew, or Islamic calendars:

@table @kbd
@item i h d
@code{diary-hebrew-insert-entry}
@item i h m
@code{diary-hebrew-insert-monthly-entry}
@item i h y
@code{diary-hebrew-insert-yearly-entry}
@item i i d
@code{diary-islamic-insert-entry}
@item i i m
@code{diary-islamic-insert-monthly-entry}
@item i i y
@code{diary-islamic-insert-yearly-entry}
@item i B d
@code{diary-bahai-insert-entry}
@item i B m
@code{diary-bahai-insert-monthly-entry}
@item i B y
@code{diary-bahai-insert-yearly-entry}
@end table

@findex diary-hebrew-insert-entry
@findex diary-hebrew-insert-monthly-entry
@findex diary-hebrew-insert-yearly-entry
@findex diary-islamic-insert-entry
@findex diary-islamic-insert-monthly-entry
@findex diary-islamic-insert-yearly-entry
@findex diary-bahai-insert-entry
@findex diary-bahai-insert-monthly-entry
@findex diary-bahai-insert-yearly-entry
  These commands work much like the corresponding commands for ordinary
diary entries: they apply to the date that point is on in the calendar
window, and what they do is insert just the date portion of a diary
entry at the end of your diary file.  You must then insert the rest of
the diary entry.  The basic commands add an entry for the specific
non-Gregorian date, the @samp{monthly} commands for the given
non-Gregorian day-within-month in every month, and the @samp{yearly}
commands for the given non-Gregorian day and month in every year.

@node Diary Display
@subsection Diary Display
@vindex diary-display-function
@findex diary-simple-display
@findex diary-fancy-display
@cindex diary buffer

  Diary display works by preparing the list of diary entries and then
running the function specified by the variable
@code{diary-display-function}.  The default value
@code{diary-fancy-display} displays diary entries and holidays by
copying them into a special buffer that exists only for the sake of
display.  Copying diary entries to a separate buffer provides an
opportunity to change the displayed text to make it prettier---for
example, to sort the entries by the dates they apply to.

@vindex diary-list-include-blanks
  Ordinarily, the fancy diary buffer does not show days for which there
are no diary entries, even if that day is a holiday.  If you want such
days to be shown in the fancy diary buffer, set the variable
@code{diary-list-include-blanks} to @code{t}.@refill

@c View mode does not seem to be described in the manual.
@c buffers.texi has a brief mention.
  The fancy diary buffer enables View mode, a minor mode that provides
commands for scrolling and searching the text.  For example, @key{SPC}
and @key{DEL} scroll forward and backward, and @key{s} starts an
incremental search.  See the documentation of the function
@code{view-mode} for more information.

  The alternative display method @code{diary-simple-display} shows the
actual diary buffer, and uses invisible text to hide entries that don't
apply.  Holidays are shown in the mode line.  The advantage of this
method is that you can edit the buffer and save your changes directly to
the diary file.  This method is not as flexible as the fancy method,
however.  For example, it cannot sort entries.  Another disadvantage is
that invisible text can be confusing.  For example, if you copy a region
of text in order to paste it elsewhere, invisible text may be included.
Similarly, since the diary buffer as you see it is an illusion, simply
printing the buffer may not print what you see on your screen.

@vindex diary-print-entries-hook
@findex diary-print-entries
  For this reason, there is a special command to print hard copy of the
diary buffer @emph{as it appears}; this command is @kbd{M-x
diary-print-entries}.  It works with either display method, although
with the fancy display you can also print the buffer like any other.  To
print a hard copy of a day-by-day diary for a week, position point on
the first day of the week, type @kbd{7 d}, and then do @kbd{M-x
diary-print-entries}.  As usual, the inclusion of the holidays slows
down the display slightly; you can speed things up by setting the
variable @code{diary-show-holidays-flag} to @code{nil}.

  This command prepares a temporary buffer that contains only the diary
entries currently visible in the diary buffer.  Unlike with the simple
display, the other irrelevant entries are really absent, not just
hidden.  After preparing the buffer, it runs the hook
@code{diary-print-entries-hook}.  The default value of this hook sends
the data directly to the printer with the command @code{lpr-buffer}
(@pxref{Printing}).  If you want to use a different command to do the
printing, just change the value of this hook.  Other uses might include,
for example, rearranging the lines into order by day and time.

  You can edit the diary entries as they appear in the simple diary
window, but it is important to remember that the buffer displayed
contains the @emph{entire} diary file, with portions of it concealed
from view.  This means, for instance, that the @kbd{C-f}
(@code{forward-char}) command can put point at what appears to be the
end of the line, but what is in reality the middle of some concealed
line.

  @emph{Be careful when editing the diary entries in the simple display!}
Inserting additional lines or adding/deleting characters in the middle
of a visible line cannot cause problems, but editing at the end of a
line may not do what you expect.  Deleting a line may delete other
invisible entries that follow it.  Before editing the simple diary
buffer, it is best to display the entire file with @kbd{s}
(@code{diary-show-all-entries}).

@node Fancy Diary Display
@subsection Fancy Diary Display

The following features only work with the fancy diary display.

@cindex sorting diary entries
  You can use the normal hook @code{diary-list-entries-hook} to sort
each day's diary entries by their time of day.  Here's how:

@findex diary-sort-entries
@example
(add-hook 'diary-list-entries-hook 'diary-sort-entries t)
@end example

@noindent
For each day, this sorts diary entries that begin with a recognizable
time of day according to their times.  Diary entries without times come
first within each day.  Note how the sort command is placed at the end
of the hook list, in case earlier members of the list change the order
of the diary entries, or add items.

@vindex diary-include-string
  Your main diary file can include other files.  This permits a group of
people to share a diary file for events that apply to all of them.
Lines in the diary file starting with @code{diary-include-string}:

@smallexample
#include "@var{filename}"
@end smallexample

@noindent
include the diary entries from the file @var{filename} in the fancy
diary buffer.  The include mechanism is recursive, so that included
files can include other files, and so on (you must be careful not to
have a cycle of inclusions, of course).  Here is how to enable the
include facility:

@vindex diary-list-entries-hook
@vindex diary-mark-entries-hook
@findex diary-include-other-diary-files
@findex diary-mark-included-diary-files
@smallexample
(add-hook 'diary-list-entries-hook 'diary-include-other-diary-files)
(add-hook 'diary-mark-entries-hook 'diary-mark-included-diary-files)
@end smallexample

The include mechanism works only with the fancy diary display, because
simple diary display shows the entries directly from your diary file.

@node Sexp Diary Entries
@subsection Sexp Entries and the Fancy Diary Display
@cindex sexp diary entries

@vindex diary-sexp-entry-symbol
  Sexp diary entries allow you to do more than just have complicated
conditions under which a diary entry applies.  Sexp entries should be
preceded by @code{diary-sexp-entry-symbol} (default @samp{%%}) in the
diary file.  With the fancy diary display, sexp entries can generate the
text of the entry depending on the date itself.

For example, an anniversary diary entry can insert
the number of years since the anniversary date into the text of the
diary entry.  Thus the @samp{%d} in this diary entry:

@findex diary-anniversary
@smallexample
%%(diary-anniversary 10 31 1948) Arthur's birthday (%d years old)
@end smallexample

@noindent
gets replaced by the age, so on October 31, 1990 the entry appears in
the fancy diary buffer like this:

@smallexample
Arthur's birthday (42 years old)
@end smallexample

@noindent
If the diary file instead contains this entry:

@smallexample
%%(diary-anniversary 10 31 1948) Arthur's %d%s birthday
@end smallexample

@noindent
the entry in the fancy diary buffer for October 31, 1990 appears like this:

@smallexample
Arthur's 42nd birthday
@end smallexample

  Similarly, cyclic diary entries can interpolate the number of repetitions
that have occurred:

@findex diary-cyclic
@smallexample
%%(diary-cyclic 50 1 1 1990) Renew medication (%d%s time)
@end smallexample

@noindent
looks like this:

@smallexample
Renew medication (5th time)
@end smallexample

@noindent
in the fancy diary display on September 8, 1990.

  There is an early reminder diary sexp that includes its entry in the
diary not only on the date of occurrence, but also on earlier dates.
For example, if you want a reminder a week before your anniversary, you
can use

@findex diary-remind
@smallexample
%%(diary-remind '(diary-anniversary 12 22 1968) 7) Ed's anniversary
@end smallexample

@noindent
and the fancy diary will show @samp{Ed's anniversary} both on December
15 and on December 22.

@findex diary-date
  The function @code{diary-date} applies to dates described by a month,
day, year combination, each of which can be an integer, a list of
integers, or @code{t} (meaning all values).  For example,

@smallexample
%%(diary-date '(10 11 12) 22 t) Rake leaves
@end smallexample

@noindent
causes the fancy diary to show

@smallexample
Rake leaves
@end smallexample

@noindent
on October 22, November 22, and December 22 of every year.

@findex diary-float
  The function @code{diary-float} allows you to describe diary entries
that apply to dates like the third Friday of November, or the last
Tuesday in April.  The parameters are the @var{month}, @var{dayname},
and an index @var{n}.  The entry appears on the @var{n}th @var{dayname}
after the first day of @var{month}, where @var{dayname}=0 means Sunday,
1 means Monday, and so on.  If @var{n} is negative it counts backward
from the end of @var{month}.  The value of @var{month} can be a list of
months, a single month, or @code{t} to specify all months.  You can also
use an optional parameter @var{day} to specify the @var{n}th
@var{dayname} on or after/before @var{day} of @var{month}; the value of
@var{day} defaults to 1 if @var{n} is positive and to the last day of
@var{month} if @var{n} is negative.  For example,

@smallexample
%%(diary-float t 1 -1) Pay rent
@end smallexample

@noindent
causes the fancy diary to show

@smallexample
Pay rent
@end smallexample

@noindent
on the last Monday of every month.

  The generality of sexp diary entries lets you specify any diary
entry that you can describe algorithmically.  A sexp diary entry
contains an expression that computes whether the entry applies to any
given date.  If its value is non-@code{nil}, the entry applies to that
date; otherwise, it does not.  The expression can use the variable
@code{date} to find the date being considered; its value is a list
(@var{month} @var{day} @var{year}) that refers to the Gregorian
calendar.

  The sexp diary entry applies to a date when the expression's value
is non-@code{nil}, but some values have more specific meanings.  If
the value is a string, that string is a description of the event which
occurs on that date.  The value can also have the form
@code{(@var{mark} . @var{string})}; then @var{mark} specifies how to
mark the date in the calendar, and @var{string} is the description of
the event.  If @var{mark} is a single-character string, that character
appears next to the date in the calendar.  If @var{mark} is a face
name, the date is displayed in that face.  If @var{mark} is
@code{nil}, that specifies no particular highlighting for the date.

  Suppose you get paid on the 21st of the month if it is a weekday, and
on the Friday before if the 21st is on a weekend.  Here is how to write
a sexp diary entry that matches those dates:

@smallexample
&%%(let ((dayname (calendar-day-of-week date))
         (day (cadr date)))
      (or (and (= day 21) (memq dayname '(1 2 3 4 5)))
          (and (memq day '(19 20)) (= dayname 5)))
         ) Pay check deposited
@end smallexample

  The following sexp diary entries take advantage of the ability (in the fancy
diary display) to concoct diary entries whose text varies based on the date:

@findex diary-sunrise-sunset
@findex diary-lunar-phases
@findex diary-day-of-year
@findex diary-iso-date
@findex diary-julian-date
@findex diary-astro-day-number
@findex diary-bahai-date
@findex diary-chinese-date
@findex diary-coptic-date
@findex diary-ethiopic-date
@findex diary-hebrew-date
@findex diary-islamic-date
@findex diary-french-date
@findex diary-mayan-date
@findex diary-persian-date
@table @code
@item %%(diary-sunrise-sunset)
Make a diary entry for today's local times of sunrise and sunset.
@item %%(diary-lunar-phases)
Make a diary entry for the phases (quarters) of the moon.
@item %%(diary-day-of-year)
Make a diary entry with today's day number in the current year and the number
of days remaining in the current year.
@item %%(diary-iso-date)
Make a diary entry with today's equivalent ISO commercial date.
@item %%(diary-julian-date)
Make a diary entry with today's equivalent Julian calendar date.
@item %%(diary-astro-day-number)
Make a diary entry with today's equivalent astronomical (Julian) day number.
@item %%(diary-bahai-date)
Make a diary entry with today's equivalent Baha'i calendar date.
@item %%(diary-chinese-date)
Make a diary entry with today's equivalent Chinese calendar date.
@item %%(diary-coptic-date)
Make a diary entry with today's equivalent Coptic calendar date.
@item %%(diary-ethiopic-date)
Make a diary entry with today's equivalent Ethiopic calendar date.
@item %%(diary-french-date)
Make a diary entry with today's equivalent date on the French Revolutionary
calendar.
@item %%(diary-hebrew-date)
Make a diary entry with today's equivalent Hebrew calendar date.
@item %%(diary-islamic-date)
Make a diary entry with today's equivalent Islamic calendar date.
@item %%(diary-mayan-date)
Make a diary entry with today's equivalent Mayan calendar date.
@item %%(diary-persian-date)
Make a diary entry with today's equivalent Persian calendar date.
@end table

@noindent
For example, including the diary entry

@smallexample
&%%(diary-hebrew-date)
@end smallexample

@noindent
causes every day's diary display to contain the equivalent date on the
Hebrew calendar, if you are using the fancy diary display.  (With simple
diary display, the literal line @samp{&%%(diary-hebrew-date)} appears in
the diary for any date.)

  This function has been used to construct certain standard Hebrew sexp
diary entries:

@cindex rosh hodesh
@findex diary-hebrew-rosh-hodesh
@cindex parasha, weekly
@findex diary-hebrew-parasha
@cindex candle lighting times
@findex diary-hebrew-sabbath-candles
@cindex omer count
@findex diary-hebrew-omer
@cindex yahrzeits
@findex diary-hebrew-yahrzeit
@table @code
@item %%(diary-hebrew-rosh-hodesh)
Make a diary entry that tells the occurrence and ritual announcement of each
new Hebrew month.
@item %%(diary-hebrew-parasha)
Make a Saturday diary entry that tells the weekly synagogue scripture reading.
@item %%(diary-hebrew-sabbath-candles)
Make a Friday diary entry that tells the @emph{local time} of Sabbath
candle lighting.
@item %%(diary-hebrew-omer)
Make a diary entry that gives the omer count, when appropriate.
@item %%(diary-hebrew-yahrzeit @var{month} @var{day} @var{year}) @var{name}
Make a diary entry marking the anniversary of a date of death.  The date
is the @emph{Gregorian} (civil) date of death.  The diary entry appears
on the proper Hebrew calendar anniversary and on the day before.  (The
order of the parameters changes according to the calendar date style;
for example in the European style to @var{day}, @var{month}, @var{year}.)
@end table

  All the functions documented above take an optional argument
@var{mark} which specifies how to mark the date in the calendar display.
If one of these functions decides that it applies to a certain date,
it returns a value that contains @var{mark}, as described above.