prop_tryhead xs = case xs of
  [] -> runner1 (enumPure1Chunk xs tryHead) == Nothing
  _  -> runner1 (enumPure1Chunk xs tryHead) == Just (P.head xs)
  where types = xs :: [Int]
prop_tryhead xs = case xs of
  [] -> runner1 (enumPure1Chunk xs tryHead) == Nothing
  _  -> runner1 (enumPure1Chunk xs tryHead) == Just (P.head xs)
  where types = xs :: [Int]
prop_tryhead xs = case xs of
  [] -> runner1 (enumPure1Chunk xs tryHead) == Nothing
  _  -> runner1 (enumPure1Chunk xs tryHead) == Just (P.head xs)
  where types = xs :: [Int]