[racket] querying the machine's system time...

The documentation is certainly inconsistent: `current-seconds' claims
to platform-specific, `current-inexact-milliseconds' claims to be since
1970, and `seconds->date' claims to work with both.

I think the right documentation repair is that `current-seconds'
results are actually portable, and ditto for
`file-or-directory-modify-seconds'. I'll double-check and fix the docs.

I'll also look into the leap-second issue. I worry about the potential
to break old code if I change the contract, but probably its ok in this
case (i.e., code that breaks would have to be strange).

At Tue, 19 Jun 2012 15:19:16 +0200, Pierpaolo Bernardi wrote:
> On Sat, Jun 16, 2012 at 6:23 AM, Matthew Flatt <mflatt at cs.utah.edu> wrote:
> > I'm confused by the question. Maybe you have and old version where 
> 'seconds->date' accepts only integers? The current version accepts a real, and 
> so fractional seconds can be in the argument to 'seconds->date'.
> 
> BTW, related to seconds->date, but not to the original question. From
> seconds->date documentation:
> 
> "The value returned by current-seconds or
> file-or-directory-modify-seconds is not portable among platforms.
> Convert a time in seconds using seconds->date when portability is
> needed."
> 
> Making this value portable only requires an addition, so why not make
> it portable?
> 
> and: "For the second field, values of 60 and 61 are for unusual, but
> possible for leap-seconds."
> 
> AFAIK, there cannot be more than one leap-second in a minute
> (actually, more than one in a month), so I believe the correct range
> should be 0..60.  (I also believe there's a typo in the quoted
> sentence).
> 
> Cheers
> P.
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