Get Unix / Epoch time as Int

Question

Is there a function in haskell for epoch time in seconds / milliseconds ?

perhaps something similar to java's

System.currentTimeMillis();

edit: as Int or Integer?

Answer 1

Yes.

getCurrentTime :: IO UTCTime.

UNIX epoch time could be retrieved as Int like that:

> :m + Data.Time System.Locale Control.Applicative
> epoch_int <- (read <$> formatTime defaultTimeLocale "%s" <$> getCurrentTime) :: IO Int
> epoch_int
1375025861

UPD: as other users noticed, there is much more simple way to do that:

> :m + Data.Time.Clock.POSIX
> round `fmap` getPOSIXTime 
1375040716
it :: Integer

Answer 2

Try this:

import Data.Time
import Data.Time.Clock.POSIX

t = getPOSIXTime

It has 6 decimal places of accuracy.

Answer 3

How about:

import Data.Time.Clock.POSIX (getPOSIXTime)

timeNanos, timeMicros, timeMillis :: IO Integer

t mul = round . (mul *) <$> getPOSIXTime
timeNanos  = t 1000000000
timeMicros = t 1000000
timeMillis = t 1000

main = do
  tNanos  <- timeNanos
  tMicros <- timeMicros
  tMillis <- timeMillis

  print tNanos
  print tMicros
  print tMillis

-- OUT:
-- 1539161680010615122
-- 1539161680010617
-- 1539161680011

Answer 4

There is also the solution discussed in Real World Haskell:

import System.Time
getClockTime >>= (\(TOD sec _) -> return sec)

Answer 5

import Data.Time.Clock.POSIX

f :: Integral b => IO b
f = getCurrentTime >>= pure . (1000*) . utcTimeToPOSIXSeconds >>= pure . round

Round is to get integer which is not actually mandatory...

original answer was without (1000*) - now is fixed

Answer 6

This works:

import System.IO.Unsafe
import Data.Time.Clock.POSIX

time = round (unsafePerformIO getPOSIXTime) :: Int

unsafePerformIO extracts time from the IO monad. Rounding to Int then yields the desired result.

UPDATE: In my Haskell web applications, I sometimes use unsafePerformIO to populate HTML checkbox and radio button forms with random numbers and hidden time stamps. Sometimes my text field and textbox forms allow users (players of interactive games) to provide data such as arbitrary numbers and dates. Justin, I trust that you don't think the user-supplied values are safer than the random numbers and time stamps I supply to the forms? And I hope you don't think I meant to imply, "Use things like unsafePerformIO if you don't understand what you're doing."

Web browsers use HTML, CSS and Javascript. You can't "keep it in the IO monad", and the browsers don't perform more or less safely depending on how the values they receive came out of Haskell monads.

Justin, for the benefit of everyone who reads this page, I ask you to reconsider and say if you still think I "really shouldn't be using unsafePerformIO this way"? My mind is open. I just don't have a clue as to what, if anything, I might be doing wrong in my work, or why readers should be discouraged from learning from me by the two down votes.

P.S. I've heard that one shouldn't say #@!% in front of the children, or in mixed company. Did I publish the "U" word where newbies might see it? Heaven forbid! -DS