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Re: [Scheme-reports] Date/time package

John J Foerch scripsit:

> Question: what do you mean by the terms "julian" and "gregorian"?

Those plus the ISO and TAI chronologies are all proleptic, and I have
added language to that effect.

>   Astronomical year numbering: includes a year zero.  Used in
>   astronomy.

The ISO chronology has astronomical years, a Monday week-start, and
numbers its centuries in Italian style (century 15 is 1500-1599).

> As a general-purpose library, it would be nice for the user to be able
> to specify all of these things, depending on the application.  (I have
> genealogy and astronomy applications in mind.)

As I noted, there is no portable way to specify a new base chronology.

> There is also the can of worms of when the gregorian reform was
> adopted in different countries.  If a person wants to work with
> historical dates, it would be important to be able to express these
> differences as different chronologies.

Hence make-compound-chronology.

> On a related topic, formatting, there was some discussion in this
> thread about how the ISO8601 is closely tied to its particular
> chronology.

Well, at least to Western-style chronologies.  It wouldn't be hard
to adapt 8601 notation to represent the second hour of 6 Sivan 5772,
which is two hours after the start of this year's festival of Shavuot,
or two hours after local sundown on 26 May 2012 Gregorian, but nobody
has actually done it.

A witness cannot give evidence of his           John Cowan
age unless he can remember being born.          cowan@x
  --Judge Blagden                               http://www.ccil.org/~cowan

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