Cookbook/Dates And Time: Difference between revisions

Revision as of 14:33, 12 January 2014

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)

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

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

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)

@@ Line 19: / Line 19: @@
 |  [http://hackage.haskell.org/packages/archive/time/latest/doc/html/Data-Time-Calendar.html#v%3AaddDays addDays]
 |<haskell>
-import Date.Time
+import Data.Time
 a = fromGregorian 2009 12 31    --> 2009-12-31
 b = addDays 1 a                 --> 2010-01-01
@@ Line 27: / Line 27: @@
 |  [http://hackage.haskell.org/packages/archive/time/latest/doc/html/Data-Time-Calendar.html#v%3AaddDays addDays]
 |<haskell>
-import Date.Time
+import Data.Time
 a = fromGregorian 2009 12 31    --> 2009-12-31
 b = addDays (-7) a              --> 2009-12-24
@@ Line 44: / Line 44: @@
 |  [http://hackage.haskell.org/packages/archive/time/latest/doc/html/Data-Time-Calendar.html#v%3AdiffDays diffDays]
 |<haskell>
-import Date.Time
+import Data.Time
 a = fromGregorian 2009 12 31    --> 2009-12-31
 b = fromGregorian 2010 12 31    --> 2010-12-31