Proposal: Add parsing (and some other changes) to the time package

[Bjorn Bringert]

There haven't been any responses to this proposal for over a week  
now, which I interpret as consent and/or indifference. I will push  
the implemented features and fixed bugs to http://darcs.haskell.org/ 
packages/time/ and then start implementing the rest (when I find the  
time).

/Björn

On 16 nov 2006, at 14.56, Bjorn Bringert wrote:

> I propose adding parsing to the time package. I also propose some  
> minor
> other changes and bugfixes. I have implemented the changes that I  
> consider
> reasonably clear-cut. The rest I will implement after community input.
>
> All already implemented changes are available from:
> http://www.cs.chalmers.se/~bringert/darcs/time/
>
> All objections, comments, etc. are welcome. I especially would like  
> feedback on the
> unimplemented enhancements, and any objections to the already  
> implemented ones.
>
> I have created ticket #1007 to track this proposal: http:// 
> hackage.haskell.org/trac/ghc/ticket/1007
>
> Proposal:
>
> == Executive summary ==
> (see below for more details).
>
> === Implemented enhancements ===
>
> * Add time parsing to the time package, including Read instances.
>
> * Add fromMondayStartWeek and fromSundayStartWeek.
>
> * Add secondsToDiffTime and picosecondsToDiffTime.
>
> === Unimplemented enhancements ===
>
> * Change %S to: the number of whole seconds.
>
> * Add %q: the number of picoseconds (including trailing zeroes).
>
> * Add %Q: decimal point and second decimals, without trailing zeros.
>
> * Add %f: The century part of the week date year.
>
> * Change %Z to produce the time zone offset if the time zone name  
> is "".
>
> * Add Eq and Ord instances for ZonedTime?
>
> * Add Typeable and Data instances for all the time package types.
>
> === Fixed bugs ===
>
> * formatTime "%c" did not include the time zone when applied to  
> ZonedTime or UTCTime.
>
> * s/propleptic/proleptic/ in some Haddock comments.
>
> * formatTime documentation of range of %U and %W was wrong, should  
> include 00.
>
> * The showWeekDate Haddock comment was missing the example.
>
> * The taiEpoch Haddock comment was missing the epoch time.
>
> === Unfixed bugs ===
>
> * Haddock comments for toJulianYearAndDay and isJulianLeapYear talk  
> about the Gregorian calendar.
>
>
> == Details ==
>
> === Implemented enhancements ===
>
> * Add time parsing to the time package.
>
> Rationale:
> The old System.Time has had a TODO  "* add functions to parse  
> strings to
> `CalendarTime' (some day...)" for a long time. The question about  
> date parsing
> comes up once in a while on the mailing lists
> (e.g. http://comments.gmane.org/gmane.comp.lang.haskell.cafe/16438).
>
> * Add fromMondayStartWeek and fromSundayStartWeek to  
> Data.Time.Calendar.OrdinalDate.
>
> Rationale:
> I can't find any duals of mondayStartWeek and sundayStartWeek. They
> are useful when implementing parsing for %W and %U.
>
> * Add secondsToDiffTime and picosecondsToDiffTime.
>
> Rationale:
> As has come up on haskell-cafe
> (http://comments.gmane.org/gmane.comp.lang.haskell.cafe/15653), it
> takes a while to figure out how to make DiffTime values.
>
> secondsToDiffTime is not that important since it is just another name
> for fromInteger, but I suspect that it would be used a lot.  Using
> fromRational to create a DiffTime from a number of picoseconds is a
> bit of a hassle, so having a picosecondsToDiffTime would be useful.
>
>
>
> === Unimplemented enhancements ===
>
> * formatTime: Change %S to: the number of whole seconds.
> * formatTime: Add %q: the number of picoseconds (including trailing  
> zeroes).
> * formatTime: Add %Q: decimal point and second decimals, without  
> trailing zeros.
> If the number of picoseconds is zero, nothing is produced (not even  
> the decimal point).
>
> Rationale:
> Currently %S includes decimals if there are any. This is different
> from strftime, and there is no format specifier for just the integer
> part of the seconds. It would be nice to have such a specifier to
> implement many standard date formats (e.g. RFC 822). Also a specifier
> for second decimals would also help when using %s. Currently there is
> no reasonable way to get more than integer second precision with
> since-epoch timestamps.  Thus the current %S would be equivalent to
> %S%Q under this proposal.
>
>
> * Add %f: The century part of the week date year.
>
> Rationale:
> There is a %g specifier for the last two digits of the week date  
> year, but no specifier
> for the century. %C cannot be used, since the normal century and  
> the week date
> century can differ:
> {{{
> > formatTime defaultTimeLocale "%Y %G" (fromGregorian 2000 1 1)
> "2000 1999"
> }}}
>
> * Change %Z to produce the time zone offset if the time zone name  
> is "".
>
> Rationale:
> Without this, if you format a ZonedTime which contains an unnamed  
> timezone,
> %Z produces the empty string. This is invalid in many formats. It  
> would be better
> to output the offset when there is no timezone name.
>
>
> * Add Eq and Ord instances for ZonedTime?
>
> Rationale:
> It's useful at least for the QuickCheck properties, but probably also
> elsewhere. There are lots of standard functions that want Eq and Ord.
>
> Problems:
>
> Should ZonedTimes be converted to UTC and compared, or should times in
> different timezones never be equal? I would argue for the latter, but
> I suspect that this problem is the reason why it never got included in
> the first place.
>
> Interestingly, there is a derived instance of Eq for TimeZone, which
> means that timezones with the same offset but different names are
> considered different. Following this logic, I think that ZonedTimes
> with different timezones should also be different. This should be
> noted in the documentation.
>
> * Add Typeable and Data instances for all the time package types.
>
> Rationale:
> It's useful and doesn't hurt anyone.
>
>
> === Fixed bugs ===
>
> * formatTime "%c" does not include the time zone even when applied  
> to ZonedTime
> or UTCTime, since "%c" is handled by the FormatTime LocalTime  
> instance:
>
> {{{
> > fmap (formatTime System.Locale.defaultTimeLocale "%c") getZonedTime
> "Sat Nov 11 19:12:45.395568  2006"
> > fmap (formatTime System.Locale.defaultTimeLocale "%c")  
> getCurrentTime
> "Sat Nov 11 18:13:52.010944  2006"
> }}}
>
> * s/propleptic/proleptic/ in Data/Time/Calendar/JulianYearDay.hs  
> and Data/Time/Calendar/OrdinalDate.hs
>
> * formatTime documentation of range of %U and %W was wrong, should  
> include 00.
>
> * The showWeekDate haddock comment is:  "show in ISO 8601 Week Date  
> format as yyyy-Www-dd (e.g."
>
> * The taiEpoch haddock comment is just "The epoch of TAI, which is"
>
>
> === Unfixed bugs ===
>
> * The haddock comments for toJulianYearAndDay and isJulianLeapYear in
> Data.Time.Calendar.JulianYearDay talk about the proleptic Gregorian  
> calendar.
> This looks like a copy-and-paste problem. What is the calendar  
> called? Proleptic Julian?
>
>
> /Björn Bringert
>
> _______________________________________________
> Libraries mailing list
> Libraries at haskell.org
> http://www.haskell.org/mailman/listinfo/libraries