On 30.08.2018 at 22:33, Kurt Weber wrote:
> The calendar conversion functions currently support (via Julian Day
> Numbers as an intermediary) conversion between Gregorian, Julian,
> Hebrew, and French Revolutionary calendars. Conspicuously absent is
> the Islamic calendar. A comment in ext/calendar/sdncal.h seems to
> suggest that the original author(s) intended to implement at some
> point, but never got around to it.
>
> The Islamic calendar offers some complications because in most
> places and communities that use it for religious purposes, the switch
> from one month to the next is based on actually observing the moon in
> the proper phase. In theory the date of this change can be
> calculated (and indeed the early Islamic surge in study of astronomy
> was motivated by the wish to know about when they should start
> looking), but tradition still demands that it be actually observed
> before a change is made--the actual impact of this is that local sky
> or weather conditions can sometimes interfere with the observation in
> a particular jurisdiction, meaning that often it comes a day or so
> later than when it otherwise would.
>
> Consequently, what I'm proposing is the Tabular Islamic Calendar,
> which was specifically created to be predictable and calculable. It
> is of limited use for religious purposes (and documentation should
> probably be clear about this), but it would be useful for, e.g.
> people working with historical documents from Islamic communities or
> groups (In fact, this is how I came to this problem--I am working on
> a Ph.D. in Russian history, and as a side project I'm developing a
> PHP-backed website to manage research notes and other information;
> because I work on prerevolutionary Russia I'm very familiar with the
> issue of needing to convert between calendar systems (in my case,
> Julian and Gregorian), and my colleagues working on Islamic history
> often have similar issues.).
>
> Tabular Islamic calendar is not ideal, but it seems like the only
> realistic option for automated conversion.
>
> As far as implementation goes, I could do it. I've already
> implemented conversion one way, before I stopped work in case there
> were issues that come up in this discussion that I hadn't foreseen
> (unfortunately, that happened roughly at the time the mailing list
> server seems to have died, so it's been paused for a couple of
> weeks). So all I'd have to do is the other direction, and it'd be
> ready to test.
Thanks! I'm not opposed to this suggestion. There is the suspended
feature request #27453[1], and I agree that even a tabular Islamic
calendar would be much more useful than the French Revolunationary calendar.
Presently, I see three counter-arguments:
(a) already supported by ext/intl
(b) maintenance burden
(c) opening up a can of worms
Ad (a): Islamic calendars are already supported by the
intl extension[2]. Even though ext/intl supports an Islamic calendar,
that doesn't prohibit that ext/calendar also does, though, since they
are independent extensions (cf. ext/mbstring, ext/iconv, ext/recode).
Ad (b): if nobody else is willing to step up as maintainer of
ext/calendar[3], I'd be willing to do so. I've already did some
maintenance[4] so far.
Ad (c): this is somewhat of a problem. I can easily imagine folks
requesting support for specific Islamic calendars which would require
(up-to-date) data, what could easily blow ext/calendar out of
proportion. Also I can imagine people coming up with “the FOO calendar
is used more widely than the tabular Islamic calendar, so it should be
supported as well” argument.
Especially due to (c) I suggest to go through the RFC process[5],
whereby the RFC could also set some precendence/rules for potentially
further calendar systems (i.e. what ext/calendar may support, and what not).
[1] <https://bugs.php.net/bug.php?id=27453>
[2]
<http://icu-project.org/apiref/icu4j/com/ibm/icu/util/IslamicCalendar.html>
[3]
<https://github.com/php/php-src/blob/7956722cfd96fdc244e9ed3dd13e162094be09cd/EXTENSIONS#L257>
[4]
<https://bugs.php.net/search.php?cmd=display&package_name[]=Calendar+related&direction=DESC&limit=30&assign=cmb&status=All&reorder_by=ts2>
[5] <https://wiki.php.net/rfc/howto>
--
Christoph M. Becker
