I am playing with Test.Hspec and Test.QuickCheck and I am traying to implement KMeans algorithm as a training. I use very simple representation of vectors: type LVector=[Double] I have no problems to write testcases with some concreate examples of input and expected output: it "sum of vectors is computed field by field" $ do (*sumVect* [[1.0, 2.0], [3.0, 4.0], [4, 5]]) `shouldBe` [8.0, 11.0] or simple properties based tests: it "zeroVector contains just zeroes" $ property (\(Positive d) -> [] == filter (/= 0.0) (*zeroVector*d) ) but I get sticked, when I try to create QuickCheck test, for example for the first case (*sumVect*). How can I generate list of lists, where all the included lists are of the same length? Link for some tutorial *) can be, I believe, enough but I would be glad for any help. Thanks Ondra @satai Nekola ondra@nekola.cz *) Maybe I have not trained my google good enough yet, but lack of tutorials describing more than the most basic usecase is probably the most problematic point in re-learning Haskell so far.