Date and Time

Syntax#

addDays :: Integer -> Day -> Day
diffDays :: Day -> Day -> Integer

fromGregorian :: Integer -> Int -> Int -> Day

 convert from proleptic Gregorian calendar. First argument is year, second month number (1-12), third day (1-31). Invalid values will be clipped to the correct range, month first, then day.

getCurrentTime :: IO UTCTime

Remarks#

The Data.Time module from time package provides support for retrieving & manipulating date & time values:

Finding Today’s Date

Current date and time can be found with getCurrentTime:

import Data.Time

print =<< getCurrentTime
-- 2016-08-02 12:05:08.937169 UTC

Alternatively, just the date is returned by fromGregorian:

fromGregorian 1984 11 17  -- yields a Day

Adding, Subtracting and Comparing Days

Given a Day, we can perform simple arithmetic and comparisons, such as adding:

import Data.Time

addDays 1 (fromGregorian 2000 1 1)
-- 2000-01-02
addDays 1 (fromGregorian 2000 12 31)
-- 2001-01-01

Subtract:

addDays (-1) (fromGregorian 2000 1 1)
-- 1999-12-31

addDays (-1) (fromGregorian 0 1 1)
-- -0001-12-31
-- wat

and even find the difference:

diffDays (fromGregorian 2000 12 31) (fromGregorian 2000 1 1)
365

note that the order matters:

diffDays (fromGregorian 2000 1 1) (fromGregorian 2000 12 31)
-365