[r6rs-discuss] [Scheme-reports] Date and time arithmetic library proposal for R7RS large Scheme
cowan at mercury.ccil.org
Mon Nov 29 17:15:12 EST 2010
Thomas Bushnell, BSG scripsit:
> If the interface says "number of seconds since the epoch, not counting leap
> seconds" (which is what Posix's gettimeofday is), then let it be that. "Add
> 1" to the value means "add one second". The precision is about the precision
> of the particular numeric representation.
Anything described as "number of seconds" is evidently an integer,
since we count things with integers. And yet you say not to think
> Remember to separate the exactness of a numeric representation from the
> accuracy of the underlying clock. If the accuracy is 10ms (typical for lots
> of systems), then that does not mean it's pointless for the numeric
> representation to be exact. So I agree that there should be no
> recommendation about what sort of numeric format to use. Keep in mind that
> "inexact rational" does not mean "floating point" in Scheme.
In principle, no; in practice, it definitely does. There are no Schemes
out there which use something other than floats for inexact rationals,
and the great bulk of them use 64-bit IEEE floats only.
> I think we should have a interface for it, but alas, Linux and Posix don't
> provide a way to get it. Given NTP and the granularity of clock interrupts,
> the accuracy is known in some sense to the system as a whole, but in
> practice difficult to determine.
It sounds like you are talking about precision, not accuracy. If the
clock is off by a day because I botched setting it, do you expect the
system to know that and report it?
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