Taylor R Campbell scripsit: > Systems that implement SECONDS-SINCE-UTC-EPOCH using a POSIX clock > should document that users must be prepared to tolerate a clock in > error by more than 1 SI second.
To say so would be disingenuous, since trying to implement SECONDS-SINCE- UTC-EPOCH with a Posix clock alone means users must be prepared to tolerate a clock in error by *any* number of SI seconds. Better to return #f and have done with it. In short: We need two sources of current time, one that counts SI seconds or fractions thereof with some epoch, and another that is relatable to the Julian Day, a measure of calendrical time. Posix time is readily available and convertible to calendrical time at the expense of not counting in SI seconds. Arbitrary-epoch time is convertible to TAI if you know a single implementation-dependent constant, and if the epoch is close to the present, it puts precision in the peripresent where it's needed, not in the past where it usually isn't. That's why TimeCowan provides current-posix-second, which also returns leap-second information if known, and current-jiffy, which is a count of implementation-dependent fractions of a second since an implementation-dependent epoch. -- John Cowan http://ccil.org/~cowan [email protected] Economists were put on this planet to make astrologers look good. --Leo McGarry _______________________________________________ Scheme-reports mailing list [email protected] http://lists.scheme-reports.org/cgi-bin/mailman/listinfo/scheme-reports
