[Haskell-cafe] Quickcheck: Help on non trivial test

Arnaud Bailly arnaud.oqube at gmail.com
Thu Jun 23 11:18:38 CEST 2011

```Hello,
What if the '2' that appears in splitPos is itself generated (ie. an int
parameter of splitFunGen) and you replace `div` by `mod`? Sorry, I have no
code to show right now.

HTH
Arnaud

On Thu, Jun 23, 2011 at 10:58 AM, jean-christophe mincke <
jeanchristophe.mincke at gmail.com> wrote:

> Hello Café,
>
> I am using quicheck for some kind of non trivial tests.
>
> The general form of these tesst is summarized by the following code.
>
>
> -- Function to be tested. Given a list of splitting functions, split the
> given list
> process :: [a] -> [[a] -> [a]] -> [a]
> process l splitFuns =
>     List.foldl proc l splitFuns
>     where
>     proc l splitFun = splitFun l
>
> -- a split function generator
> splitFunGen :: Gen ([a] -> [a])
> splitFunGen = return \$ proc
>                       where
>                       proc l = let splitPos = List.length l `div` 2 --
> Problem I would like  splitPos = some random value between [0 and length of
> l]
>                                   in fst \$ List.splitAt splitPos l
>
> splitFunsGen :: Gen  [[a] -> [a]]
> splitFunsGen = vectorOf 20 splitFunGen
>
> instance Show a => Show ([a] -> [a]) where
>     show _ = " a split fun "
>
> r = quickCheck \$ forAll splitFunsGen prop
>     where
>     prop splitFuns = let l = process [1..100] splitFuns
>                             in List.length l >= 0 -- dummy test here for
> the sake of example
>
>
> The process to be tested takes a list that is randomly perturbated
> (spitFuns). The result of each perturbation is fed into the next
> perturbation.
>
> Ideally I would like the perturbating function to depend on the previous
> perturbated list (see computation of splitPos in splitFunGen).
>
> I am not sure how I could use quickcheck in this case.
>
> Has anyone a better idea?
>
> Thanks
>
> J-C
>
>
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