Hi, This is one of those topics everybody else seems to be familiar with, but which I don't quite understand, and can't seem to find any good information about. I have a function declared as: anova2 :: (Fractional c, Ord b) => [a->b] -> (a->c) -> [a] -> [Anova1 c] where the first parameter is a list of classifiers. I could simplify it, I guess, to something like classify :: Eq b => [a->b] -> [a] -> [[[a]]] classify cs xs = ... where for each classifying function in cs, I would get the xs partitioned accordingly. E.g. classify [fst,snd] [(1,0), (1,2), (2,0)] would yield [ [(1,0), (1,2)], [(2,0)] -- classified by `fst` , [(1,0), (2,0)], [(1,2)]] -- classified by `snd` Now, obviously, the problem is that fst and snd, being passed in a list, needs to be of the same type; this complicates classifying a list of type [(Int,Bool)], for instance¹. I have a vague notion this is solvable using quantifiers (since I ever only use Eq operations on the type), but I'm not sure exactly how, I can't seem to find a good tutorial, and my Monte-Carlo programming approach doesn't seem to be leading anywhere :-) Can somebody suggest a solution, or a place to look? -kzm ¹ I guess I can convert Bool to Int (True->1, False->0), but it's not very appealing, IMHO. -- If I haven't seen further, it is by standing in the footprints of giants