Re: Text collation

[Carl Witty]

On Tue, 2006-12-05 at 11:20 +1100, Kevin Ryde wrote:
> address@hidden (Ludovic Courtès) writes:
> > I don't clearly understand.  Could you provide more details for the
> > novice (perhaps in another thread)?  :-)
> 
> The note in the manual:
> 
>       *Caution*: The current code in this module incorrectly extends
>       the Gregorian calendar leap year rule back prior to the
>       introduction of those reforms in 1582 (or the appropriate year
>       in various countries).  The Julian calendar was used prior to
>       1582, and there were 10 days skipped for the reform, but the
>       code doesn't implement that.
> 
> So for instance the year 1500 should be a leap year, but isn't in the
> current code.  (If I've got that right off the top of my head ... :-)

If I understand correctly, this would make date->julian-day (for
instance) convert from Julian calendar dates before 1582 and Gregorian
calendar dates after 1582.  This is cute, but I don't think it's
particularly useful; the problem is that the Julian to Gregorian switch
lasted for hundreds of years around the world (and, indeed, some
churches still use the Julian calendar to determine religious dates), so
you can't tell if a date is Julian or Gregorian just by looking at the
year.  I would propose leaving the code the way it is now, and changing
the note to something like "Note: Dates in this module use the proleptic
Gregorian calendar, which means that it extends the Gregorian calendar
leap year rule back prior to the introduction of these reforms in 1582."
(See http://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar for more
information on the proleptic Gregorian calendar.)

If people need to use Julian dates, then there should be a separate
julian-date type with separate converters.

Carl Witty