A demonstration of using QuickCheck to test C code

quickcheck_c.hs

-- This is a snippet cut-and-paste from a larger code body, might not compile or
-- work as expected as such

import Prelude hiding (pi)

import Data.Bits
import Data.Word (Word32)

import Foreign.C.Types (CSize)
import Foreign.Marshal.Array (withArrayLen)
import Foreign.Marshal.Utils (with)
import Foreign.Ptr (Ptr)
import Foreign.Storable (peek)

import Test.QuickCheck

foreign import ccall unsafe "hashword" fHashWord
    :: Ptr Word32 -> CSize -> Word32 -> IO Word32

-- | A wrapper for native 'hashword'
hashWord :: [Word32]   -- ^ Input values to hash
         -> Word32     -- ^ Initial salt
         -> IO Word32  -- ^ Hash result
hashWord as i = withArrayLen as $ \l p -> fHashWord p (fromIntegral l) i

foreign import ccall unsafe "hashword2" fHashWord2
    :: Ptr Word32 -> CSize -> Ptr Word32 -> Ptr Word32 -> IO ()

-- | A wrapper for native 'hashword2'
hashWord2 :: [Word32]             -- ^ Input values to hash
          -> Word32               -- ^ First salt
          -> Word32               -- ^ Second salt
          -> IO (Word32, Word32)  -- ^ Hashes
hashWord2 as i j = withArrayLen as $ \las pas ->
    with i $ \pi -> do
        j' <- with j $ \pj -> do
            fHashWord2 pas (fromIntegral las) pi pj
            peek pj

        i' <- peek pi
        return (i', j')

prop_hashword_fst_hashword2 :: [Word32] -> Word32  -> IO Bool
prop_hashword_fst_hashword2 a i = do
    h <- hashWord a i
    h' <- fst `fmap` hashWord2 a i 0

    return $ h == h'

main = quickCheck (prop_hashword_fst_hashword2 :: [Word32] -> Word32 -> IO Bool)