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

[John Cowan <cowan@x>]

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
about integers.

> 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?

-- 
First known example of political correctness:   John Cowan
After Nurhachi had united all the other         http://www.ccil.org/~cowan
Jurchen tribes under the leadership of the      cowan@x
Manchus, his successor Abahai (1592-1643)
issued an order that the name Jurchen should       --S. Robert Ramsey,
be banned, and from then on, they were all           The Languages of China
to be called Manchus.

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