[r6rs-discuss] Date and time arithmetic library proposal for R7RS large Scheme

[r6rsguy at free-comp-shop.com]

> From: John Cowan <cowan at mercury.ccil.org>
> Cc: r6rsguy at free-comp-shop.com, discuss at r6rs.org
> 
> Ray Dillinger scripsit:
> 
> > > On reflection I agree, and the current version (version 17) of
> > > TimeCowan now makes (current-posix-second) an integer.  I have
> > > updated TimeAdvancedCowan to version 15 to reflect this change.
> > 
> > I do not understand why this is so.  Can you explain it for me?
> 
> Because what happens at the subsecond level is not well-defined,
> and insofar as it is well-defined, it is not well-implemented.
> Theoretically the repeat happens exactly at the change from 23:60
> to 23:61, but NTP does it several fractions of a second later.

A nitpick or typo, but there is no 23:61.  Seconds within a minute are
numbered from zero (a very good convention) and so the sixty-first
(leap) second is 23:59:60.  Most days end with 23:59:59 and change to
00:00:00 of the next day one SI second later.

I do not think there is any "repeat" in NTP.  NTP transmits time as an
integer count of seconds, a fractional second, and a leap second
warning.  It is up to the client (user) software to break this into
hh:mm:ss form and insert the leap in the proper place or (more likely)
torque it up.

Posix has a repeat, the cause of all our grievances.

   -- Keith