Thanks, it sent me to the (higly probably) right direction: newtype RectList = RectList [LVector] deriving Show instance Arbitrary RectList where arbitrary = do m <- getPositive <$> arbitrary n <- getPositive <$> arbitrary RectList <$> replicateM n (vector m) and the test can look like this: it "average times number is sum" $ property (\(RectList x) -> null $ nozeroMembers $ zipWith (-) ( map (* (fromIntegral $ length x)) (average x)) (sumVect x) ) Thanks again Ondrej

On 2015-02-15 at 10:52, Ondrej Nekola wrote:

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How can I generate list of lists, where all the included lists are of the same length? The general approach is to make a newtype, the Arbitrary instance of which does what you want. For example, QucickCheck includes newtypes Positive[1] and NonNegative[2], that generate restricted numbers.

For your case, I'd write something like (untested):

``` newtype RectList a = RectList [[a]]

instance Arbitrary a => Arbitrary RectList a where arbitrary = do -- length of inner lists m <- getPositive <$> arbitrary -- length of outer list, can be zero n <- getNonNegative <$> arbitrary RectList <$> replicateM n (vector m) ```

vector here is another function provided by QuickCheck: [3].

Hope this helps.

bergey

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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. _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners Footnotes: [1] http://hackage.haskell.org/package/QuickCheck-2.7.6/docs/Test-QuickCheck.htm...

[2] http://hackage.haskell.org/package/QuickCheck-2.7.6/docs/Test-QuickCheck.htm...

[3] http://hackage.haskell.org/package/QuickCheck-2.7.6/docs/Test-QuickCheck-Arb...