RFC: Time Library 0.1

[Ashley Yakeley]

Sorry for the hiatus, my job has left less free time to work on this.

Please take a look at a first attempt at writing a replacement for the 
standard time library.
http://semantic.org/TimeLib/

Take a look at the Haddock documentation:
http://semantic.org/TimeLib/doc/html/

Download the source:
http://semantic.org/TimeLib/TimeLib-0.1.tar.gz

Or keep up-to-date:
darcs get http://semantic.org/TimeLib/TimeLib/

It needs GHC 6.4. Just run "make" to build the library, tests and 
documentation. There's also a cabal file (as a completely separate build 
process), but I've been having trouble with that on Mac OS X.

I'm particularly interested in comments from people who try to write 
little applications for it. What did you have trouble with? What made no 
sense?

Some points:

1. There is no leap second table provided, though there is a type 
(LeapSecondTable) for such things. Any software compiled with a fixed 
table would soon become out of date.

2. There is no table of time-zones provided, since these also change. 
However, if there's a good way of getting this from the TZ database on 
the machine, I'll add that.

It is actually possible to get the local time-zone for any given time, 
indeed one of the test programs finds your local summertime transitions. 
The Timezone type includes name, minutes of offset, and a "summertime" 
flag.

3. I allow multiple calendars with the DayEncoding class. GregorianDay 
is the most obvious instance, but there are some other useful ones such 
as ISOWeek. And anyone interested in local cultural calendars can plug 
their own in here.

4. The TimeLocale type comes from the already existing System.Locale.

5. I've tried to balance simplicity and functionality. Of course, the 
majority of people will only be interested in ordinary Gregorian date 
and time, so I have a simple CalendarTime type synonym with associated 
functions:
http://semantic.org/TimeLib/doc/html/System.Time.Calendar.html#8

6. It's not possible to expunge POSIX time. I've hidden it, but it's 
used behind the scenes. Why? Because it's the only way to do sensible 
arithmetic on UTC times without knowing the leap second table and 
without worrying about one-second offsets.

7. I include Data.Fixed which provides a fixed-point arithmetic type 
(wrapper around Integer). It probably should be in a separate package. 
It allows dealing with seconds as a single thing, rather than as an 
integer/picoseconds pair.

8. I don't have any text-parsing functionality. This is a fair amount of 
work, so it would be good to know sensible requirements.

-- 
Ashley Yakeley, Seattle WA