[Haskell-cafe] Re: Working with multiple time zones

[Dave Hinton]

Hurrah, I am now calling the C function tzset() from my Haskell code
via FFI, and I'm getting the results I want.

$ cat hsc2now.hs
{-# LANGUAGE ForeignFunctionInterface #-}
import Data.Time
import Data.Time.LocalTime
import System.Environment
import System.Posix.Env
foreign import ccall "time.h tzset" tzset :: IO ()
outTime utc tzName
  = do putEnv ("TZ=" ++ tzName)
       tzset
       tz <- getTimeZone utc
       putStrLn (tzName ++ "\t" ++ show (utcToLocalTime tz utc))
main
  = do utc <- getCurrentTime
       mapM_ (outTime utc) =<< getArgs
$ ghc --make hsc2now.hs -o hsc2now
[1 of 1] Compiling Main             ( hsc2now.hs, hsc2now.o )
Linking hsc2now ...
$ ./hsc2now Europe/Moscow Europe/Paris Europe/London
Europe/Moscow   2008-02-17 22:06:44.770153
Europe/Paris    2008-02-17 20:06:44.770153
Europe/London   2008-02-17 19:06:44.770153

Thank you everyone for your help :-)