14  Dates and Times

module Time ( ClockTime,  Month(January,February,March,April,May,June,       July,August,September,October,November,December), Day(Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday), CalendarTime(CalendarTime, ctYear, ctMonth, ctDay, ctHour, ctMin,      ctPicosec, ctWDay, ctYDay, ctTZName, ctTZ, ctIsDST), TimeDiff(TimeDiff, tdYear, tdMonth, tdDay, tdHour,  tdMin, tdSec, tdPicosec), getClockTime, addToClockTime, diffClockTimes,         toCalendarTime, toUTCTime, toClockTime,         calendarTimeToString, formatCalendarTime ) where import Ix(Ix) data ClockTime = ... -- Implementation-dependent instance Ord  ClockTime where ... instance Eq   ClockTime where ... data Month =  January   | February | March    | April            |  May       | June     | July     | August            |  September | October  | November | December            deriving (Eq, Ord, Enum, Bounded, Ix, Read, Show) data Day   =  Sunday | Monday  | Tuesday  | Wednesday | Thursday             |  Friday | Saturday            deriving (Eq, Ord, Enum, Bounded, Ix, Read, Show) data CalendarTime = CalendarTime { ctYear   :: Int,         ctMonth  :: Month,         ctDay, ctHour, ctMin, ctSec  :: Int, ctPicosec :: Integer, ctWDay    :: Day, ctYDay       :: Int, ctTZName   :: String, ctTZ          :: Int, ctIsDST :: Bool } deriving (Eq, Ord, Read, Show) data TimeDiff = TimeDiff { tdYear, tdMonth, tdDay, tdHour, tdMin, tdSec :: Int, tdPicosec      :: Integer } deriving (Eq, Ord, Read, Show)

-- Functions on times getClockTime         :: IO ClockTime       addToClockTime       :: TimeDiff  -> ClockTime -> ClockTime diffClockTimes       :: ClockTime -> ClockTime -> TimeDiff       toCalendarTime       :: ClockTime    -> IO CalendarTime toUTCTime            :: ClockTime    -> CalendarTime toClockTime          :: CalendarTime -> ClockTime calendarTimeToString :: CalendarTime -> String formatCalendarTime   :: TimeLocale -> String -> CalendarTime -> String

The Time library provides standard functionality for clock times, including timezone information. It follows RFC 1129 in its use of Coordinated Universal Time (UTC).

ClockTime is an abstract type, used for the system's internal clock time. Clock times may be compared directly or converted to a calendar time CalendarTime for I/O or other manipulations. CalendarTime is a user-readable and manipulable representation of the internal ClockTime type. The numeric fields have the following ranges.

Value Range Comments ctYear -maxInt... maxInt Pre-Gregorian dates are inaccurate ctDay 1... 31 ctHour 0... 23 ctMin 0... 59 ctSec 0... 61 Allows for two Leap Seconds ctPicosec 0... (1012)-1 ctYDay 0... 365 364 in non-Leap years ctTZ -89999... 89999 Variation from UTC in seconds

The ctTZName field is the name of the time zone. The ctIsDST field is True if Daylight Savings Time would be in effect, and False otherwise. The TimeDiff type records the difference between two clock times in a user-readable way.

Function getClockTime returns the current time in its internal representation. The expression addToClockTime d t adds a time difference d and a clock time t to yield a new clock time. The difference d may be either positive or negative. The expression diffClockTimes t1 t2 returns the difference between two clock times t1 and t2 as a TimeDiff.

Function toCalendarTime t converts t to a local time, modified by the timezone and daylight savings time settings in force at the time of conversion. Because of this dependence on the local environment, toCalendarTime is in the IO monad.

Function toUTCTime t converts t into a CalendarTime in standard UTC format. toClockTime l converts l into the corresponding internal ClockTime ignoring the contents of the ctWDay, ctYDay, ctTZName, and ctIsDST fields.

Function calendarTimeToString formats calendar times using local conventions and a formatting string.

14.1  Library Time