From: David Rogers <davidandrewrogers@gmail.com>
To: Org-mode list <emacs-orgmode@gnu.org>
Subject: Diary sexp and comparing dates, agenda
Date: Thu, 11 Jan 2024 21:58:05 -0800 [thread overview]
Message-ID: <rzhwmsfhz4i.fsf@gmail.com> (raw)
Hello all
I'm using the Org agenda to show when certain church occasions
will happen. Mostly I've got them working correctly, after
"stealing" the method used in holidays.el for finding the date of
Easter, along with someone else's function that then uses that to
find the difference between Easter and today. (I'm pretty sure
that whole idea was on emacswiki, and I think Paul Sexton put it
together.)
So now I have a much smaller problem to solve, but I don't
understand how to get it to work; I suspect it has to do with how
dates get formatted within different functions. Using what I
already have, I can do this:
* Example 1
<%%(= 245 (mf-days-from-easter))>
because "mf-days-from-easter" is defined in my init file, along
with the definition of Easter itself. This does what it looks like
it should do; this year, Example 1 is shown on December 1.
And I can do
* Example 2
<%%(and (diary-float 1 0 5 7) (<= (mf-days-from-easter) -56))>
to say "five Sundays after January 6th, but only if Easter is
still 8 weeks away or more".
But Example 1 isn't quite finished, because that date is too close
to Christmas. I can easily show a diary sexp defining when "too
close to Christmas" is:
<%%(diary-float 12 0 -4 24)>
So I want to combine these ideas, to say "Show Example 1 in the
agenda 245 days after Easter each year, but only if it's earlier
than the fourth Sunday before Christmas".
I could do a long string of (and (not this day, not this day, etc
etc [insert long list of days] . . . , but that seems like a last
resort.
Everything in this question fits into "the current year according
to the agenda view" - there's no need to consider dates that cross
a year boundary.
So: Is there a fairly simple way to define a (mf-days-from-advent)
that will do a similar job to what (mf-days-from-easter) is
already doing (i.e. it works when used in a diary sexp)?
Here are the relevant definitions I've been using:
(defun mf-easter (displayed-year)
(let* ((century (1+ (/ displayed-year 100)))
(shifted-epact ; age of moon for
April 5...
(% (+ 14 (* 11 (% displayed-year 19)) ; ...by
Nicaean rule
(- ; ...corrected for the Gregorian
century rule
(/ (* 3 century) 4))
(/ ; ...corrected for Metonic cycle
inaccuracy
(+ 5 (* 8 century)) 25)
(* 30 century)) ; keeps value positive
30))
(adjusted-epact ; adjust for 29.5 day
month
(if (or (zerop shifted-epact)
(and (= shifted-epact 1) (< 10 (%
displayed-year 19))))
(1+ shifted-epact)
shifted-epact))
(paschal-moon ; day after the full moon on or after
March 21
(- (calendar-absolute-from-gregorian (list 4 19
displayed-year))
adjusted-epact)))
(calendar-dayname-on-or-before 0 (+ paschal-moon
7))))
(defun mf-days-from-easter ()
"When used in a diary sexp, this function will calculate how
many days
are between the current date (DATE) and Easter Sunday."
(- (calendar-absolute-from-gregorian date)
(mf-easter (calendar-extract-year date))))
--
David
next reply other threads:[~2024-01-12 5:59 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-12 5:58 David Rogers [this message]
2024-01-12 17:01 ` Diary sexp and comparing dates, agenda Tory S. Anderson
2024-01-12 18:11 ` Ken Mankoff
2024-01-12 23:00 ` Ihor Radchenko
2024-01-13 5:41 ` David Rogers
2024-01-13 20:05 ` Ihor Radchenko
2024-01-13 23:44 ` David Rogers
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