Re: [Haskell-cafe] Converting string to System.Time.ClockTime

8 Dec 2011

      Ok, maybe you could advise what packages to use for this simple scenario:

I have two text strings with dates:
s1 = "Wed, 07 Dec 2011 10:09:21 +0000"
s2 = "Wed, 07 Dec 2011 10:11:00 +0000"

I need:
1) Find how many seconds are between  these dates
2) Calculate the date in the middle between these dates
3) Print out all three dates in the different format, like these:
 2011,  7 Dec, Wed, 10:11:00

What functions should I use to implement this?

On Thu, Dec 8, 2011 at 7:13 PM, Antoine Latter  wrote:
...
On Thu, Dec 8, 2011 at 9:01 AM, dokondr  wrote:
...
Now, when I have managed to convert UTCTime to seconds (see code below) I
got stuck trying to convert from UTCTime to CalendarTime, how to do this?
It might be easier to use 'diffUTCTime' and 'addUTCTime' instead of
converting to and from POSIX seconds.
What do you need the 'CalendarTime' for? I recommend not mixing the
'time' and 'old-time' packages if you can avoid it.
If you really need to for inter-operating with some other library, it
looks like you can use the 'datetime' package to convert from a
UTCTime to a ClockTime, and then you can use the 'old-time' package to
convert from a 'ClockTime' to a 'CalendarTime'.
Antoine
...
import Data.Time.Format
import Data.Time.Clock
import Locale
import Data.Maybe
import Data.Time.Clock.POSIX
s1 = "Wed, 07 Dec 2011 10:09:21 +0000"
s2 = "Wed, 07 Dec 2011 10:11:00 +0000"
t1 = fromJust $ tryParseTime s1
t2 = fromJust $ tryParseTime s2
pt1 = utcTimeToPOSIXSeconds t1  -- :: UTCTime -> POSIXTime
pt2 = utcTimeToPOSIXSeconds t2
pt3 = pt1 + (pt2 - pt1) / 2
t3 = posixSecondsToUTCTime pt3
t = compare t1 t2
tryParseTime :: String -> Maybe UTCTime
tryParseTime timeStr = tryFormat (parseTime defaultTimeLocale timeFormat1
timeStr :: Maybe UTCTime)
   where
     tryFormat time
        | time == Nothing = parseTime defaultTimeLocale timeFormat2
timeStr
:: Maybe UTCTime
        | otherwise = time
timeFormat1 = "%a, %d %b %Y %T %z"
     timeFormat2 = "%m/%e/%Y %l:%M:%S %p"
-- timeFormat1 = "%m/%d/%Y %l:%M:%S %p"
On Thu, Dec 8, 2011 at 6:30 PM, dokondr  wrote:
...
I need to parse time strings like "Wed, 07 Dec 2011 10:09:21 +0000" to a
type that:
1) implements Eq, Ord
2) is numerical, so I could subtract one value from another to find the
difference or interval length
To answer 1) requirement I wrote the following snippet. Yet I could not
subtract  UTCTime values. How can I convert them to milliseconds?
import Data.Time.Format
import Data.Time.Clock
import Locale
import Data.Maybe
s1 = "Wed, 07 Dec 2011 10:09:21 +0000"
s2 = "Wed, 07 Dec 2011 10:11:00 +0000"
t1 = fromJust $ tryParseTime s1
t2 = fromJust $ tryParseTime s2
t = compare t1 t2
tryParseTime :: String -> Maybe UTCTime
tryParseTime timeStr = tryFormat (parseTime defaultTimeLocale
timeFormat1
...
timeStr :: Maybe UTCTime)
   where
     tryFormat time
        | time == Nothing = parseTime defaultTimeLocale timeFormat2
timeStr :: Maybe UTCTime
        | otherwise = time
timeFormat1 = "%a, %d %b %Y %T %z"
     timeFormat2 = "%m/%e/%Y %l:%M:%S %p"
On Thu, Dec 8, 2011 at 6:12 PM, Erik Hesselink 
wrote:
...
I'm not sure if you really need ClockTime (from old-time), but if you
don't, the types from the 'time' package are all parseable with
`parseTime` [1].
Erik
[1]
http://hackage.haskell.org/packages/archive/time/latest/doc/html/Data-Time-F...
...
On Thu, Dec 8, 2011 at 14:16, dokondr  wrote:
...
Hi,
What would be the simplest way to convert strings like "Wed, 07 Dec
2011
10:09:21 +0000" to System.Time.ClockTime ?
Thanks!