prop_mapChunksM_ xs n = n > 0 ==>
 snd (runWriter ((enumSpecial xs n (Iter.mapChunksM_ f)) >>= run))
 == Sum (P.length xs)
  where f ck = tell (Sum $ P.length ck)
        types = xs :: [Int]
prop_mapChunksM_ xs n = n > 0 ==>
 snd (runWriter ((enumSpecial xs n (Iter.mapChunksM_ f)) >>= run))
 == Sum (P.length xs)
  where f ck = tell (Sum $ P.length ck)
        types = xs :: [Int]
prop_mapChunksM_ xs n = n > 0 ==>
 snd (runWriter ((enumSpecial xs n (Iter.mapChunksM_ f)) >>= run))
 == Sum (P.length xs)
  where f ck = tell (Sum $ P.length ck)
        types = xs :: [Int]