prop_peek xs = runner1 (enumPure1Chunk xs peek) == sHead xs
  where
  types = xs :: [Int]
  sHead [] = Nothing
  sHead (x:_) = Just x
prop_peek xs = runner1 (enumPure1Chunk xs peek) == sHead xs
  where
  types = xs :: [Int]
  sHead [] = Nothing
  sHead (x:_) = Just x
prop_peek xs = runner1 (enumPure1Chunk xs peek) == sHead xs
  where
  types = xs :: [Int]
  sHead [] = Nothing
  sHead (x:_) = Just x