Re: [Haskell-cafe] class Arbitrary in quickcheck

On 5 May 2010 11:38, Tim Docker wrote:

On 5 May 2010 09:01, Ozgur Akgun wrote:

...

your quick check property (in a different way of writing) is the following:

prop_1 :: Maybe Double -> Bool prop_1 v = v == v

I think you misunderstood me. The property was fabricated just for the example.

OK that's possible :)

My question was why, when I generate random values for (Maybe t, Maybe t) using the Arbitrary type class, do I always see two Nothing values or two Just values, and never one of each?

Let me try to understand you then. What happens when you run the following command in ghci? sample (arbitrary :: Gen (Maybe Int, Maybe Int) ) Do you still always get (Just _, Just _) or (Nothing, Nothing) pairs, or do you also get some (Nothing, Just _) or (Just _, Nothing) pairs? Ozgur