Hello Café, I am using quicheck for some kind of non trivial tests. The general form of these tesst is summarized by the following code. -- Function to be tested. Given a list of splitting functions, split the given list process :: [a] -> [[a] -> [a]] -> [a] process l splitFuns = List.foldl proc l splitFuns where proc l splitFun = splitFun l -- a split function generator splitFunGen :: Gen ([a] -> [a]) splitFunGen = return $ proc where proc l = let splitPos = List.length l `div` 2 -- Problem I would like splitPos = some random value between [0 and length of l] in fst $ List.splitAt splitPos l splitFunsGen :: Gen [[a] -> [a]] splitFunsGen = vectorOf 20 splitFunGen instance Show a => Show ([a] -> [a]) where show _ = " a split fun " r = quickCheck $ forAll splitFunsGen prop where prop splitFuns = let l = process [1..100] splitFuns in List.length l >= 0 -- dummy test here for the sake of example The process to be tested takes a list that is randomly perturbated (spitFuns). The result of each perturbation is fed into the next perturbation. Ideally I would like the perturbating function to depend on the previous perturbated list (see computation of splitPos in splitFunGen). I am not sure how I could use quickcheck in this case. Has anyone a better idea? Thanks J-C