[Haskell-cafe] Quickcheck

[Iustin Pop]

On Mon, Nov 12, 2012 at 10:14:30PM +0100, Simon Hengel wrote:
> On Mon, Nov 12, 2012 at 07:21:06PM +0000, graham at fatlazycat.com wrote:
> > Hi, 
> > 
> > Trying to find some good docs on QuickCheck, if anyone has one ?
> > 
> > Been scanning what I can find, but a question.
> > 
> > What would be the best way to generate two different/distinct integers ?
> 
> I would use Quickcheck's implication operator here:
> 
>     quickCheck $ \x y -> x /= (y :: Int) ==> ...

That's good, but it only eliminates test cases after they have been
generated. A slightly better (IMHO) version is to generate "correct"
values in the first place:

    prop_Test :: Property
    prop_Test =
	  forAll (arbitrary::Gen Int) $ \x ->
	  forAll (arbitrary `suchThat` (/= x)) $ \y ->
	  …

regards,
iustin