prop_heads2 xs = runner1 (enumPure1Chunk xs $ heads [] >>= \c ->
                          stream2list >>= \s -> return (c,s))
                 == (0, xs)
  where types = xs :: [Int]
prop_heads2 xs = runner1 (enumPure1Chunk xs $ heads [] >>= \c ->
                          stream2list >>= \s -> return (c,s))
                 == (0, xs)
  where types = xs :: [Int]
prop_heads2 xs = runner1 (enumPure1Chunk xs $ heads [] >>= \c ->
                          stream2list >>= \s -> return (c,s))
                 == (0, xs)
  where types = xs :: [Int]