A basic PRNG based on the Heys' cipher

HeysPRNG.hs

import HeysCipher
import Data.ByteString as B
import Data.Bits
import Data.Word
import System.Environment

main = do
    [arg, filename] <- getArgs
    let bytes = read arg :: Integer
    let randomBytes = (B.pack . genBytes . read) arg
    B.writeFile filename randomBytes

genBytes :: Int -> [Word8]

genBytes count 
    | count <= 0 = []
    | otherwise = rWord8_first : rWord8_last : genBytes (count - 2)
    where
    rWord16 = crypt (0,0,0) (fromIntegral count)
    rWord8_first = (fromIntegral :: Word16 -> Word8) rWord16 `shiftR` 8
    rWord8_last =  (fromIntegral :: Word16 -> Word8) rWord16 .&. 0xff