hugs vs. nhc98 in toClockTime

[Donn Cave]

Malcolm Wallace <malcolm@cs.york.ac.uk> wrote,
| The maintainers of nhc98, ghc, and Hugs, are working hard to remove
| any remaining differences in the libraries.  So, if you find such
| differences, do please report them to us.

The year value input to Time toClockTime is years since 1900, for
nhc98, but years since 0 for hugs.

As long as the value has to be represented in a 32 bit time_t,
the range of valid years doesn't overlap, so it may be possible
to support both usages.  Python does that.

I find another difference in toClockTime, which I think is really
kind of a bug.  I haven't looked at the source to see how it happens.
If I supply ctTZ value that is different from the local time zone,
it affects the result.  I think this is not really right, but what's
worse, the offset seems backwards.  I'm in PDT, -25200 -- that's
what comes out of toCalendarTime, -7 * 3600.  If I supply a CDT
offset, -5 * 3600 = -18000, the result time comes out 2 hours
_later_, calculated in PDT.  I could be confused about this - the
sun rises in the East, the way I figure it, and when it's 6 AM there,
it's 4 AM here - not 8 AM.

$ runhugs cal.hs 2003
CalendarTime{ctYear=2003,ctMonth=May,ctDay=1,ctHour=5,ctMin=45,ctSec=0,ctPicosec=0,ctWDay=Thursday,ctYDay=0,ctTZName="",ctTZ=-18000,ctIsDST=True}
-> Thu May  1 07:45:00 PDT 2003
-> CalendarTime{ctYear=2003,ctMonth=May,ctDay=1,ctHour=7,ctMin=45,ctSec=0,ctPicosec=0,ctWDay=Thursday,ctYDay=120,ctTZName="PDT",ctTZ=-25200,ctIsDST=True}

	Donn Cave, University Computing Services, University of Washington
	donn@u.washington.edu
-----------------------------
main = do
        let calt = CalendarTime {
                        ctYear = 2003,
                        ctMonth = May,
                        ctDay = 1,
                        ctHour = 5,
                        ctMin = 45,
                        ctSec = 0,
                        ctPicosec = 0,
                        ctWDay = Thursday,
                        ctYDay = 0,
                        ctTZName = "",
                        ctTZ = -7 * 3600,
                        ctIsDST = True
                }
        putStrLn (show calt)
        let clt = toClockTime calt
        putStrLn ("-> " ++ (show clt))
        cal <- toCalendarTime clt
        putStrLn ("-> " ++ (show cal))