Re: Software Engineering News Brief

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Paul Eggert says

"... which is why the next version of Ada should support Gregorian dates
all the way back to at least the year 1, if not before.  Trying to
match the historical introduction of the Gregorian calendar
leads to severe politico-technical problems.  For an example of this
see my May 1995 comp.risks article about Sybase's historically naive
practice of arbitrarily rejecting Gregorian dates before 1753."

That sounds silly to me. This is a highly specialized requirement that
should be provided by auxiliary packages, not by the central package
for dealing with near by dates that is primarily intended for use in
control of time related processing (note that Calendar is still in the
tasking chapter, even in the new RM.

Also, Gregorian dates are quite tricky, because the change over in the
calendar happened at different times in different parts of the world, so
you need detailed geo-political localization for such processing. Again,
much more suitable for some auxialiry package than for Calendar, which 
does not even have time zone support.

As for prohibiting implementations from extending the range, yes, this is
quite deliberate, but you state it in a peculiar manner. There is nothing
to stop an implementation from providing an extended calendar package
with whatever range of dates is needed, and this can easily be written s
a portable package, but you certainly do NOT want different implementations
to implement the standard library with such gratuitous variations. Ada is
much more concerned with portability than you are I guess.

If there is really a need for such extended calendar support from real
Ada programmers writing real Ada programs, rather than just in the context
of CLA discussions, then such packages will appear, along with many other
useful packages, you cannot put support for all kinds of specialized
requirements into the language. I would say this is a perfect example of
specialized needs that should NOT be met in the standard language. I would
far rather have Ada implementors working to get their implementations more
efficient and more robust than wasting time in the library trying to figure
out when the switch to Gregorian dates happened in Lithuania.

In the GNAT world, people are very free in making suggestions about things
they would like to see in GNAT. No one ever mentioned this, so I find that
at least one measure of its extremely limited value.