Hello all: I want to generate some hamming distance statistics about a set of strings. As explained in another e-mail in this list, I used the following code to call the functions: (exampl holds the list of strings of size w) filter (\x -> x /= 0) $ map (uncurry hammingX) [(xs, ys) | xs <- exampl, ys <- exampl] I have two hamming functions: -- hamming distance for variable length strings hamming :: String -> String -> Int hamming x y = hamming' x y 0 where hamming' [] _ !c = c hamming' _ [] !c = c hamming' (x:xs) (y:ys) !c | x == y = hamming' xs ys c | otherwise = hamming' xs ys (c + 1) -- function posted in this mailing list hamming2 :: String -> String -> Int hamming2 xs ys = length (filter not (zipWith (==) xs ys)) I am executing these functions millions of times and the bottleneck of my program is in them as explained by running in profiling mode with +RTS -K400M -p -RTS The costlier function is the hamming distance COST CENTRE MODULE %time %alloc hamming Distances 66.6 41.9 It says that it is performing 41% of the allocations. In the case of hamming2 the allocations go as far as 52%. I could understand that there are allocations in "hamming2" because we are creating pairs, but in the case of "hamming" there should be no allocation. How can I execute my hamming functions without allocating memory? Best regards, Arnoldo Muller