[Haskell-cafe] quickCheck problem

[Roelof Wobben]

Maybe im on the wrong track now.

I know that if three numbers are the same then the outcome will be false.
The same if two numbers are the same.

Can I not do something like this :

prop_different x y z = not( (x /= y && y /= z && x /= z))

to test all cases at once.

Roelof



Op 7-10-2015 om 00:28 schreef Rogan Creswick:
> On Tue, Oct 6, 2015 at 2:01 PM, Roelof Wobben <r.wobben at home.nl> wrote:
>> but why this part :
>>
>> x (x + y) (x - (y + 1))
> That is buggy.  I was trying to quickly create three arguments that
> are guaranteed to be different by some random amount, but what I wrote
> doesn't always work (eg: if y = 0, then the first two arguments are
> the same, if y is -1, the first and 3rd are the same, if x is MAX_INT,
> then it may or may not be the same as other arguments, depending on Y,
> etc...)
>
> The predicate guard should work, though it may take longer to run.
>
> --Rogan
>
>>
>> Roelof
>>
>> Op 6-10-2015 om 22:31 schreef Rogan Creswick:
>>> On Tue, Oct 6, 2015 at 1:24 PM, Roelof Wobben <r.wobben at home.nl> wrote:
>>>> Hello,
>>>>
>>>> I have written a function to test if three numbers are the same.
>>>>
>>>> Now I want to test my functions by using quickCheck.
>>>>
>>>> So I thought to test first if all three are the same.
>>>>
>>>> but how can I tell quickcheck that all numbers are the same.
>>> Just have quickcheck generate one number, and use it for all three
>>> arguments, eg:
>>>
>>> prop_allSame :: Int -> Bool
>>> prop_allSame x = yourFn x x x
>>>
>>> then test the other cases:
>>>
>>> prop_different :: Int -> Int -> Int -> Property
>>> prop_different x y z = x /= y && y /= z && x /= z ==> not $ yourFn x y z
>>>
>>> That's probably OK for ints, but generally the guard in that style
>>> isn't a great solution, since quickcheck will just keep generating
>>> inputs until the predicate is satisfied.  That can take a while, so
>>> you could also manually offset the first input in various ways:
>>>
>>> prop_different :: Int -> Int -> Bool
>>> prop_different x y = not $ yourFn x (x + y) (x - (y + 1)) -- I put a
>>> +1 in here to avoid returning true where y = 0,
>>>
>>> There are probably other ways to mutate a randomly generated input for
>>> your problem that may work better, but that's the general idea.
>>>
>>> --Rogan
>>>
>>>> and second question :  hwo do the test likeif two numbers are the same.
>>>>
>>>> I ask this because I try to solve a exercise of the programming Haskell
>>>> book,
>>>> IM have read chapter 3 now.
>>>>
>>>> Roelof
>>>>
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