From: Ashley Yakeley [mailto:ashley@semantic.org]
* Should we include a timezone field in CalendarTime?
Yes. If a CalendarTime doesn't carry timezone information with it, then the user must bundle it. They will want to do this because (1) they will be probably dealing with local time (2) a CalendarTime sans timezone is equivalent to UTC, and is therefore not much use (i.e. we may as well use UTC instead).
* TimeZone represents a fixed offset to UTC. What should it look like internally, and what functions on it should we provide?
There are timezones which are not integral hour offsets, so an (hours, minutes) pair, or maybe just ticks is sufficient. Or maybe a Duration (see below). Ticks is probably best from an implementation point-of-view, right? Should it include the timezone name? Although the name determines the offset, a given offset could match many names, so to preserve information we'd probably want to retain the timezone name internally. Do we want to support timezone names? Do we want to embed summer-time (daylight-savings) timezone behaviour into the library? This would obviously be useful for displaying the correct local time, but makes the timezone part of the library quite complex.
OK, so here are the basic functions of System.Time.Calendar:
utcToCalendar :: TimeZone -> UTCTime -> CalendarTime
calendarToUTC :: TimeZone -> CalendarTime -> UTCTime
CalendarTime should be a "struct", i.e. a datatype with its constructor and access functions exported.
I'm assuming System.Time.Calendar is Gregorian. How about - a Duration type - some calendar arithmetic functions - arithmetic on Durations e.g. data Duration = Duration { -- this looks familiar... durYear :: Int, durMonth :: Int, durDay :: Int, durHour :: Int, durMin :: Int, durSec :: Int, durPicosec :: Integer } deriving ... calendarAdd :: CalendarTime -> Duration -> CalendarTime calendarDiff :: CalendarTime -> CalendarTime -> Duration durationAdd :: Duration -> Duration -> Duration durationDiff :: Duration -> Duration -> Duration Alistair. ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************