CODEWITHSUNDEEP
haskelltime
QSpider
QSpider

Reputation: 567

Haskell Convert Time milliseconds to UTCTime

I have time as milliseconds since 1970-01-01 00:00 UTC. How can I convert it to UTCTime (Integer -> UTCTime)? I need UTCTime for inserting it in MongoDB.

Thank you!

Upvotes: 2

Views: 1723

Answers (2)

Jann Müller
Jann Müller

Reputation: 338

You can use the function posixSecondsToUTCTime in Data.Time.Clock.POSIX. As your value is in milliseconds you need to divide it by 1000 first. Here's an example:

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

millisToUTC :: Integer -> UTCTime
millisToUTC t = posixSecondsToUTCTime $ (fromInteger t) / 1000

Upvotes: 3

ErikR
ErikR

Reputation: 52029

Here's how to create a UTCTime and add a number of seconds to it:

import Data.Time.Calendar
import Data.Time.Clock

-- 1/1/1900 as a Day
jan_1_1900_day = fromGregorian 1900 1 1 :: Day

-- 1/1/1900 as a UTCTime
jan_1_1900_time = UTCTime jan_1_1900_day 0

secs = 86400+3600  -- number of seconds to add to 1/1/1900
                   -- = 1 day + 1 hour

-- add some seconds to 1/1/1900 00:00:00
myTime = addUTCTime (fromIntegral secs) jan_1_1900_time

showTime t = (utctDay t, utctDayTime t) -- to see inside a UTCTime

main = do
  print $ showTime jan_1_1900_time
  print $ showTime myTime

The output is:

(1900-01-01,0s)
(1900-01-02,3600s)

The first argument to addUTCTime is a NominalDiffTime which has both a Num instance and an Enum instance.

Using the Num instance, fromIntegral x will create a NominalDiffTime of x seconds.

Using the Enum instance, toEnum x will create a NominalDiffTime of x picoseconds.

So if you want millisecond resolution on your times, you can use this recipe:

millis = (2*86400+3600)*1000  -- milliseconds to add = 2 days + 1 hour

myTime' = addUTCTime (toEnum (millis*10^9)) jan_1_1900_time

And then print $ showtime myTime' results in:

(1900-01-03,3600s)

Upvotes: 1

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