I have come across this problem in a couple places, here are my solutions a parser based on Parsec (this parses RFC2822 email style dates) parseDate :: Parser ClockTime parseDate = token $ do skipOption (word >> skipOption (token $ char ',')) day <- number month <- ml year <- liftM (\n -> if n < 100 then n + 1900 else n)number hour <- number token $ char ':' minute <- number second <- option 0 ((token $ char ':') >> number) tz <- timezone spaces option () comments return $ toClockTime calendarTime { ctYear = year, ctDay = day, ctMonth = month, ctHour = hour, ctMin = minute, ctSec= second, ctTZ = tz} timezone = token $ do pm <- (char '-' >> return negate) <|> (char '+' >> return id) h1 <- liftM digitToInt digit h2 <- liftM digitToInt digit m1 <- liftM digitToInt digit m2 <- liftM digitToInt digit return $ 60 * (pm $ (h1 * 10 + h2) * 60 + m1 * 10 + m2) another solution when I just wanted to serialize times, was this instance of Binary I wrote instance Binary ClockTime where put bh ct = do let t = toUTCTime ct put bh (ctYear t) put bh (fromEnum $ ctMonth t) put bh (ctDay t) put bh (ctHour t) put bh (ctMin t) put bh (ctSec t) get bh = do year <- get bh month <- fmap toEnum $ get bh day <- get bh hour <- get bh min <- get bh sec <- get bh return $ toClockTime $ (toUTCTime epoch) {ctYear = year, ctDay = day, ctMonth = month, ctHour = hour, ctMin = min, ctSec = sec} epoch = toClockTime $ CalendarTime { ctYear = 1970, ctMonth = January, ctDay = 0, ctHour = 0, ctMin = 0, ctSec = 0, ctTZ = 0, ctPicosec = 0, ctWDay = undefined, ctYDay = undefined, ctTZName = undefined, ctIsDST = undefined} perhaps one might be useful to you... John On Fri, Oct 18, 2002 at 03:15:44PM -0400, David Roundy wrote:
I've been looking at the standard Time module, and it seems pretty easy to convert a date into a string (using either calendarTimeToString or formatCalendarTime), but there doesn't seem to be any way to reverse the process.
I understand that there are so many date and time formats that it may be hard to parse, and that for many formats there may be no unambiguous translation back into a CalendarTime (e.g. if the time zone isn't included in the string), but it seems like a pretty fundamental (and commonly needed) ability to be able to output a human-readable date and then read it back in.
Does anyone have a suggestion how best to go about this? I guess the easiest way might be to just convert to UTC and then use formatCalendarTime to choose what formatting I want and then write my own parser to reverse the process. But this seems like a process with a relatively high probability of introducing rarely seen bugs, which ought to be dealt with by a standard library.
Of course, there are also a couple of other workarounds I could use. CalendarTime derives from Show, so I could just output the result of show, but that's an awfully verbose format. I could also give up on comparing dates (which I don't necesarily need, although it is nice) and just treat dates as strings.
Any ideas or commentary would be welcome. -- David Roundy http://civet.berkeley.edu/droundy/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
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