Dear All, Definitely I am having some troubles in thinking like an haskeller... Please consider the snippet at the end of the email. Its aim is rather simple: given a list and a value i (position of along the list), it defines the "future" as the chunk of the list from i-th element of he list to the end of the list, whereas the "past" is anything in the list that appears before the i-th element. I wrote a function which checks whether lists of length 1,2...(till I reach the end of the list) in the future (always with respect to position i) has already occurred in past. In order to find the length of the longest list in the future which has already been seen in the past, I could select the "true" values in the output of function iter_find list i but this is a waste of CPU: I simply would like a while condition to tell my function to stop checking new sublists as soon as it finds one which has not occurred in the past and I would like a counter (a kind of i++) telling me how many times the process has been iterated. Any suggestion is helpful. Cheers Lorenzo ------------------------------------------------------------------- import Data.Ord import Data.List main :: IO () main = do let list = [4,55,66,77,88,99,12,9,77,88,99,12,-99] let i = 9 let b = iter_find list i putStrLn "b is, " print b is_sublist sublist list = sublist `isInfixOf` list gen_fut_list list i j = take j $ drop (i-1) list gen_past_list list i = take (i-1) list find_in_list list i j = is_sublist (gen_fut_list list i j) (gen_past_list list i) iter_find list i = map (find_in_list list i) [1..n] where n = (length list) - i +1