Hi Cafe! I am struggling with an interesting problem while defining a function. It looks quite easy to me, but I couldn't manage to have a proper implementation yet. To illustrate what I'm trying to achive, I'll introduce special cases of the desired function, and hopefully build towards a solution step by step. -- simplest case, taking 2 lists as parameters and returning a list of list containing every possible pair (but represented as lists) allPossibilities2 :: [a] -> [a] -> [[a]] allPossibilities2 listX listY = [ [x,y] | x <- listX, y <- listY] -- sample output -- allPossibilities2 [1,2,3] [7,8,9] -- [[1,7],[1,8],[1,9],[2,7],[2,8],[2,9],[3,7],[3,8],[3,9]] -- simplest case with 3 parameters instead of 2 allPossibilities3 :: [a] -> [a] -> [a] -> [[a]] allPossibilities3 listX listY listZ = [ [x,y,z] | x <- listX, y <- listY, z <- listZ] -- allPossibilities3 [1,2] [3,4,5] [6,7] -- [[1,3,6],[1,3,7],[1,4,6],[1,4,7],[1,5,6],[1,5,7],[2,3,6],[2,3,7],[2,4,6],[2,4,7],[2,5,6],[2,5,7]] These are easy and work just fine. All I want to do is to generalize this function receiving n lists as parameters and doing the simple action described above. Since I cannot pass variable number of parameters to a function, I'll use list of lists from now on. Following are the implementations of the same functions with different types (instead of two lists, a list of lists assumed to caontain those 2 elements) allPossibilities2' :: [[a]] -> [[a]] allPossibilities2' list = [ [x,y] | x <- list !! 0, y <- list !! 1] -- allPossibilities2' [[1,2,3],[7,8,9]] -- [[1,7],[1,8],[1,9],[2,7],[2,8],[2,9],[3,7],[3,8],[3,9]] allPossibilities3' :: [[a]] -> [[a]] allPossibilities3' list = [ [x,y,z] | x <- list !! 0, y <- list !! 1, z <- list !! 2] -- allPossibilities3' [[1,2],[3,4,5],[6,7]] -- [[1,3,6],[1,3,7],[1,4,6],[1,4,7],[1,5,6],[1,5,7],[2,3,6],[2,3,7],[2,4,6],[2,4,7],[2,5,6],[2,5,7]] This is ugly! Anyway, just forget the fact that these funstions do not do a check on the length of the input list for a moment. My question is, how can I generalize this function to accept a list of lists of arbitrary length, and produce the required result. I hope I managed to make my point clear enough. Waiting for suggestions. Regards, -- Ozgur Akgun