z_axis <z_a...@163.com> wrote:
> betterStdGen :: IO StdGen
> betterStdGen = alloca $ \p -> do
> h <- openBinaryFile "/dev/urandom" ReadMode
> hGetBuf h p $ sizeOf (undefined :: Int)
> hClose h
> mkStdGen <$> peek p
>
> picoSec :: IO Integer
> picoSec = do
> t <- ctPicosec `liftM` (getClockTime >>= toCalendarTime)
> return t
>
> The pseudo-code is :
>
> if doesFileExist "/dev/urandom"
> then myGen = betterStdGen
> else myGen = (mkStdGen . fromTnteger) <$> picoSec
>
> How to write these pseudo-code elegantly ?
I would do this:
{-# LANGUAGE ScopedTypeVariables #-}
readFrom :: forall a. Storable a => Handle -> IO a
readFrom h =
alloca $ \ptr ->
hGetBuf h ptr (sizeOf (undefined :: a)) >>
peek ptr
newStdGen' :: IO StdGen
newStdGen' = do
mh <- try $ openBinaryFile "/dev/urandom" ReadMode
case mh of
Left err -> ctPicosec <$> (getClockTime >>= toCalendarTime)
Right h -> mkStdGen <$> readFrom h `finally` hClose h
Warning: Untested code, but it should work and have a safer file
handling. Also note that the current implementation (base >= 4) does
this already.
You should probably try one of the more sophisticated PRNG libraries out
there. Check out mersenne-random and mwc-random. If you want a pure
generator, there is also mersenne-random-pure64 and some other
libraries.
Greets,
Ertugrul
--
nightmare = unsafePerformIO (getWrongWife >>= sex)
http://ertes.de/
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