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Data.Time.Clock

Contents

Universal Time
Absolute intervals
UTC

Description
Types and functions for UTC and UT1
Synopsis

newtype UniversalTime = ModJulianDate {

getModJulianDate :: Rational

}
data DiffTime
data UTCTime = UTCTime {

utctDay :: Day
utctDayTime :: DiffTime

}
data NominalDiffTime
addUTCTime :: NominalDiffTime -> UTCTime -> UTCTime
diffUTCTime :: UTCTime -> UTCTime -> NominalDiffTime
getCurrentTime :: IO UTCTime

Universal Time
Time as measured by the earth.
newtype UniversalTime

The Modified Julian Date is the day with the fraction of the day, measured from UT midnight. It's used to represent UT1, which is time as measured by the earth's rotation, adjusted for various wobbles.
Constructors

ModJulianDate |

getModJulianDate :: Rational |

Instances

Eq UniversalTime
Ord UniversalTime

Absolute intervals
data DiffTime

This is a length of time, as measured by a clock. Conversion functions will treat it as seconds. It has an accuracy of 10^-12 s.
Instances

Enum DiffTime
Eq DiffTime
Fractional DiffTime
Num DiffTime
Ord DiffTime
Real DiffTime
Show DiffTime

UTC
UTC is time as measured by a clock, corrected to keep pace with the earth by adding or removing occasional seconds, known as "leap seconds". These corrections are not predictable and are announced with six month's notice. No table of these corrections is provided, as any program compiled with it would become out of date in six months.

If you don't care about leap seconds, use UTCTime and NominalDiffTime for your clock calculations, and you'll be fine.

data UTCTime

This is the simplest representation of UTC. It consists of the day number, and a time offset from midnight. Note that if a day has a leap second added to it, it will have 86401 seconds.
Constructors

UTCTime |

utctDay :: Day | the day
utctDayTime :: DiffTime | the time from midnight, 0 <= t < 86401s (because of leap-seconds)

Instances

Eq UTCTime
FormatTime UTCTime
Ord UTCTime
Show UTCTime

data NominalDiffTime

This is a length of time, as measured by UTC. Conversion functions will treat it as seconds. It has an accuracy of 10^-12 s. It ignores leap-seconds, so it's not necessarily a fixed amount of clock time. For instance, 23:00 UTC + 2 hours of NominalDiffTime = 01:00 UTC (+ 1 day), regardless of whether a leap-second intervened.
Instances

Enum NominalDiffTime
Eq NominalDiffTime
Fractional NominalDiffTime
Num NominalDiffTime
Ord NominalDiffTime
Real NominalDiffTime
RealFrac NominalDiffTime
Show NominalDiffTime

addUTCTime :: NominalDiffTime -> UTCTime -> UTCTime
addUTCTime a b = a + b
diffUTCTime :: UTCTime -> UTCTime -> NominalDiffTime
diffUTCTime a b = a - b
getCurrentTime :: IO UTCTime
Get the current UTC time from the system clock.
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