[Haskell-cafe] quickCheck problem
Roelof Wobben
r.wobben at home.nl
Tue Oct 6 21:01:44 UTC 2015
Thanks,
but why this part :
x (x + y) (x - (y + 1))
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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