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

[Marc Feeley <feeley@x>]

On 2010-11-26, at 2:16 AM, John Cowan wrote:

> r6rsguy@x scripsit:
> 
>> If fractions are allowed, why count milliseconds?
> 
> Given that it should be easy to implement most dates as fixed-size
> objects, milliseconds seem like a good compromise between range and
> precision.

Please don't count time using milliseconds.  It clutters my brain to have to remember a different unit of time than plain seconds.

Moreover, the choice of milliseconds, rather than microseconds or nanoseconds is purely an artifact of the current speed of computers.  If you chose milliseconds as the unit of time in the hope of getting better resolution using integers you'll probably say 2 years from now "milliseconds aren't precise enough for these fast CPUs, lets change the spec to use microseconds", and then 20 years from now "darn! these CPUs have become fast! lets change the specs to use nanoseconds", etc.  Integers shouldn't be used for measuring time points because applications need different resolutions.

With a 64 bit float, you can represent a time interval of up to 3 months with a nanosecond resolution, and up to 266 years with a microsecond resolution.  I don't see any practical reason for wanting more than this.

Marc


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