OK, I think what you're saying is to work with (random) integers and use fromEnum and toEnum to get corresponding DayOfWeek. But I get this when I try to use toEnum: [michael@localhost ~]$ ghci dow GHCi, version 6.10.1: http://www.haskell.org/ghc/  :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main             ( dow.hs, interpreted ) Ok, modules loaded: Main. *Main> fromEnum Wednesday Loading package old-locale-1.0.0.1 ... linking ... done. Loading package old-time-1.0.0.1 ... linking ... done. Loading package random-1.0.0.1 ... linking ... done. 2 *Main> toEnum 2 *** Exception: Prelude.Enum.().toEnum: bad argument *Main> Michael --- On Fri, 5/1/09, John Van Enk wrote: From: John Van Enk Subject: Re: [Haskell-cafe] Generating random enums To: "michael rice" Cc: haskell-cafe@haskell.org Date: Friday, May 1, 2009, 12:36 PM When you derive Enum, you get fromEnum and toEnum for free. You don't need your dow2Int stuff or int2Dow. Replace those with fromEnum and toEnum respectively.   /jve On Fri, May 1, 2009 at 12:26 PM, michael rice wrote: I'm using the code below to generate random days of the week [Monday..Sunday]. Is there a better/shorter way to do this? Michael ============== [michael@localhost ~]$ ghci dow GHCi, version 6.10.1: http://www.haskell.org/ghc/  :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main             ( dow.hs, interpreted ) Ok, modules loaded: Main. *Main> random (mkStdGen 100) :: (DayOfWeek, StdGen) Loading package old-locale-1.0.0.1 ... linking ... done. Loading package old-time-1.0.0.1 ... linking ... done. Loading package random-1.0.0.1 ... linking ... done. (Friday,4041414 40692) *Main> random (mkStdGen 123) :: (DayOfWeek, StdGen) (Tuesday,4961736 40692) *Main> ============== import System.Random data DayOfWeek     = Monday     | Tuesday     | Wednesday     | Thursday     | Friday     | Saturday     | Sunday     deriving (Show, Read, Eq, Enum, Ord, Bounded) instance Random DayOfWeek where   randomR (a,b) g =       case (randomIvalInteger (toInteger (dow2Int a), toInteger (dow2Int b)) g) of         (x, g) -> (int2Dow x, g)        where          dow2Int Monday    = 0          dow2Int Tuesday   = 1          dow2Int Wednesday = 2          dow2Int Thursday  = 3          dow2Int Friday    = 4          dow2Int Saturday  = 5          dow2Int Sunday    = 6      int2Dow 0    = Monday      int2Dow 1    = Tuesday      int2Dow 2    = Wednesday      int2Dow 3    = Thursday      int2Dow 4    = Friday      int2Dow 5    = Saturday      int2Dow 6    = Sunday   random g      = randomR (minBound,maxBound) g randomIvalInteger :: (RandomGen g, Num a) => (Integer, Integer) -> g -> (a, g) randomIvalInteger (l,h) rng  | l > h     = randomIvalInteger (h,l) rng  | otherwise = case (f n 1 rng) of (v, rng') -> (fromInteger (l + v `mod` k), rng')      where        k = h - l + 1        b = 2147483561        n = iLogBase b k        f 0 acc g = (acc, g)        f n acc g =           let        (x,g')   = next g       in       f (n-1) (fromIntegral x + acc * b) g' iLogBase :: Integer -> Integer -> Integer iLogBase b i = if i < b then 1 else 1 + iLogBase b (i `div` b)   _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- /jve