The 'lens-datetime' library provides a unified lens based accessors to the various types in 'Data.Time.Clock', 'Data.Time.Calendar' and 'Data.Time.LocalTime'. This library only tries to make some of the common use-cases convenient, it doesn't aim for completeness. If you want completeness and/or efficiency try the 'thyme' package instead (<http://hackage.haskell.org/package/thyme>).
Demonstration of basic uses.
>import Control.Lens >import Data.Time >import Data.Time.Lens > >aDay :: Day >aDay = fromGregorian 2013 08 22 > >aLocal :: LocalTime >aLocal = LocalTime aDay (TimeOfDay 13 45 28) > >aUTC :: UTCTime >aUTC = UTCTime aDay 7458.9
You can then do the following:
>> aLocal ^. years >2013 >> aUTC ^. months >8 >> aLocal & time .~ midnight >2013-08-22 00:00:00 >> aUTC & days .~ 1 & months .~ 1 >2013-01-01 02:04:18.9 UTC
You can manipulate the date-time values with proper roll-over behavior via the 'FlexibleDateTime' mechanism:
>> aLocal & flexDT.months +~ 12 >2014-08-22 13:45:28 >> aUTC & flexDT.days +~ 100 >2013-11-30 02:04:18.9 UTC >> aLocal & flexDT.minutes +~ 120 >2013-08-22 15:45:28 >> aLocal & flexDT %~ ((days +~ 7) . (hours +~ 2)) >2013-08-22 13:45:28.