SoE with Data.Set

;;off https://stackoverflow.com/questions/3852764/sieve-of-eratosthenes-in-haskell/64417225#64417225
;;by https://stackoverflow.com/users/304423/evg
;;https://www.youtube.com/watch?v=kCWSVYbmIfg&feature=youtu.be

;;edit by https://stackoverflow.com/users/849891/will-ness

    import qualified Data.Set as Set (fromList, difference)

    kr n lim = (*n) <$> [2..lim `div` n]
             = [ n*x | x <- [2..div lim n]]
             = takeWhile (<= lim) [ n*x | x <- [2..]]
             = takeWhile (<= lim) [ n*2, n*3 ..]
             = takeWhile (<= lim) [ n+n, n+n+n ..]
             = [n+n, n+n+n .. lim]

    g lim = difference (fromList [2..lim]) (fromList $ concat $ (`kr` lim) <$> [2..lim])
          = difference (fromList [2..lim])
                (fromList $ concat $ [kr n lim | n <- [2..lim]])
          = difference (fromList [2..lim])
                (fromList $ concat $ [[n+n, n+n+n .. lim] | n <- [2..lim]])
          = difference (fromList [2..lim])
                (fromList $ concat $ [[n+n, n+n+n .. lim] | n <- [2..lim`div`2]])
          = difference (fromList [2..lim])
                (fromList $ concat $ takeWhile (not . null) $
                                     [[n+n, n+n+n .. lim] | n <- [2..]])
          = difference (fromList [2..lim])
                (fromList $ concat $ takeWhile (not . null) $
                                     [[n*n, n*n+n .. lim] | n <- [2..]])

          = foldl (\ a b -> difference a $ fromList b)
                  (fromList [2..lim])
                  (takeWhile (not . null) [[n*n, n*n+n .. lim] | n <- [2..]])

          = foldl (\ a b@(m:_) -> if not (Set.member m a) then a
                                  else difference a $ fromList b)
                  (fromList [2..lim])
                  (takeWhile (not . null) [[n*n, n*n+n .. lim] | n <- [2..]])

          = foldl (\ a b@(m:_) -> if not (Set.member m a) then a
                                  else difference a $ fromList b)
                  (fromList $ 2:[3,5..lim])
                  (takeWhile (not . null) [[n*n, n*n+2*n .. lim] | n <- [3,5..]])

    g lim = difference (fromList [2..lim])
                       (fromList [ m | n <- [2..lim`div`2], m <- [n+n, n+n+n .. lim]])
          = difference (fromList [2..lim])
                       (fromList [ m | n <- [2..isqrt lim], m <- [n*n, n*n+n .. lim]])
          = difference (fromList $ 2 : [3,5..lim])
                       (fromList [ m | n <- [3,5..isqrt lim], m <- [n*n, n*n+2*n .. lim]])

    g lim | lim < 2 = []
          | otherwise =
            difference (fromList $ 2 : [3,5..lim])
                       (fromList [ m | n <- drop 1 $ g (isqrt lim),
                                       m <- [n*n, n*n+2*n .. lim]])