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Cookbook/Dates And Time

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Contents

1 Finding today's date

import Data.Time
 
c <- getCurrentTime                  --> 2009-04-21 14:25:29.5585588 UTC 
(y,m,d) = toGregorian $ utctDay c    --> (2009,4,21)

2 Adding to or subtracting from a date

Problem Solution Examples
adding days to a date addDays
import Data.Time
a = fromGregorian 2009 12 31    --> 2009-12-31
b = addDays 1 a                 --> 2010-01-01
subtracting days from a date addDays
import Data.Time
a = fromGregorian 2009 12 31    --> 2009-12-31
b = addDays (-7) a              --> 2009-12-24

3 Difference of two dates

Problem Solution Examples
calculating the difference of two dates diffDays
import Data.Time
a = fromGregorian 2009 12 31    --> 2009-12-31
b = fromGregorian 2010 12 31    --> 2010-12-31
diffDays b a                    --> 365

4 CPU time

Use System.CPUTime.getCPUTime to get the CPU time in picoseconds.

You can time a computation like this

getCPUTimeDouble :: IO Double
getCPUTimeDouble = do t <- System.CPUTime.getCPUTime; return ((fromInteger t) * 1e-12)
 
main = do
    t1 <- getCPUTimeDouble
    print (fib 30)
    t2 <- getCPUTimeDouble
    print (t2-t1)