View source for Cookbook/Dates And Time

== Finding today's date ==

<haskell>
import Data.Time

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

== Adding to or subtracting from a date ==

{| class="wikitable"
|-
!  Problem
!  Solution
!  Examples
|-
|  adding days to a date
|  [http://hackage.haskell.org/packages/archive/time/latest/doc/html/Data-Time-Calendar.html#v%3AaddDays addDays]
|<haskell>
import Data.Time
a = fromGregorian 2009 12 31    --> 2009-12-31
b = addDays 1 a                 --> 2010-01-01
</haskell>
|-
|  subtracting days from a date
|  [http://hackage.haskell.org/packages/archive/time/latest/doc/html/Data-Time-Calendar.html#v%3AaddDays addDays]
|<haskell>
import Data.Time
a = fromGregorian 2009 12 31    --> 2009-12-31
b = addDays (-7) a              --> 2009-12-24
</haskell>
|}

== Difference of two dates ==

{| class="wikitable"
|-
!  Problem
!  Solution
!  Examples
|-
|  calculating the difference of two dates
|  [http://hackage.haskell.org/packages/archive/time/latest/doc/html/Data-Time-Calendar.html#v%3AdiffDays diffDays]
|<haskell>
import Data.Time
a = fromGregorian 2009 12 31    --> 2009-12-31
b = fromGregorian 2010 12 31    --> 2010-12-31
diffDays b a                    --> 365
</haskell>
|}

== CPU time ==
Use [http://www.haskell.org/ghc/docs/latest/html/libraries/base/System-CPUTime.html#v%3AgetCPUTime System.CPUTime.getCPUTime] to get the CPU time in picoseconds.

You can time a computation like this
<haskell>
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)
</haskell>