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# Re: [Scheme-reports] [r6rs-discuss] Date and time arithmetic library proposal for R7RS large Scheme

On 27 November 2010 12:05, Marc Feeley <feeley@x> wrote:
> On 2010-11-26, at 9:00 PM, John Cowan wrote:
>> Marc Feeley scripsit:
>>> Please don't count time using milliseconds.  It clutters my brain to
>>> have to remember a different unit of time than plain seconds.
>>
>> And yet the SI unit of mass is the kilogram.  But I'll think about that.
>
> I'm not sure why you bring kilograms into the discussion.  We're talking about time and the SI unit for time is the second.
>
Legal time is expressed in terms of legal seconds, and I suppose we
need legal seconds somewhere in the time library. Now, since a legal second
may be either 1 or 2 SI seconds long, it might also be a good idea to sport
a SI second or fraction thereof as an entity managed by the library, as
something DISTINCT from legal seconds.

If we can't agree on what fraction that shall be, because of portability
issues, why not introduce an implementation-dependent unit "jiffies" or
some such, and an implementation-dependent constant conversion rate
jiffies-per-second, which could be an integer, fraction, real number,
but hopefully not a complex number, and if possible exact. This would
allow embedded implementation of Scheme to use whatever the hardware
or OS clock provides them without further expensive conversion during
time-sensitive operations.

My modest proposal, for a Scheme implementation faithful to the spirit
of Scheme, of doing "The Right Thing" at the expense of respect for
convention, would be for a jiffy to be the Planck Unit of time:
tP = 5.391 24(27) × 10^−44 s
http://en.wikipedia.org/wiki/Planck_units

If R7RS is to set the duration of a jiffy for all standard-compliant
Scheme implementations, I vote for
1 jiffy = 1 tP

[ François-René ÐVB Rideau | Reflection&Cybernethics | http://fare.tunes.org ]
A fruitful discussion is a negotiation, out of which emerges meaning. Classic
works are standards, and politeness is a protocol, to ease such negotiation.
With a reasonably expressive language, neither is strictly needed,
but both sure do help, and they are where the general progress happens.

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