your quick check property (in a different way of writing) is the following: prop_1 :: Maybe Double -> Bool prop_1 v = v == v but what you want is actually the following: prop_2 :: Maybe Double -> Maybe Double -> Bool prop_2 v1 v2 = v2 == v2 if I understood the problem correctly, using prop_2 should solve it. just run verboseCheck<http://hackage.haskell.org/packages/archive/QuickCheck/1.1.0.0/doc/html/Test-QuickCheck.html#v:verboseCheck>on these two and observe the results. Best, On 5 May 2010 08:47, Tim Docker <twd2@dockerz.net> wrote:
I've notice a behaviour of quickcheck that is unexpected to me. With this code:
import Test.QuickCheck
main = check myconfig ((\v -> v == v) :: (Maybe Double,Maybe Double) -> Bool)
myconfig = defaultConfig{configMaxTest=100000, configEvery = \n args -> show n ++ ":\n" ++ unlines args}
I am relying on the default Arbitrary instances to generate pairs of maybe doubles. But to my surprise, all of the pairs have these patterns:
(Just _ Just _) (Nothing, Nothing)
I never see patterns:
(Just _, Nothing) (Nothing, Just _)
Why is this the case?
Thanks,
Tim
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