[Haskell-cafe] the purpose of QuickCheck's size parameter

[Petr Pudlák]

PS: Just to make clear, it's not that I have something against QuickCheck
or similar libraries, on the contrary, they're great! I'm just playing the
devil's advocate to analyze and understand the concept.

ne 17. 6. 2018 v 4:05 odesílatel Oleg Grenrus <oleg.grenrus at iki.fi> napsal:

> Not only avoid extremely large trees, but in general guarantee termination
> of the generation process
>
> Sent from my iPhone
>
> On 15 Jun 2018, at 0.31, David Feuer <david.feuer at gmail.com> wrote:
>
> data Foo a = Leaf a | Node [Foo a]
>
> Without the size parameter, it's a bit tricky to control the distribution
> to avoid generating extremely large trees. I certainly agree, however, that
> the size parameter is an ugly and ill-specified hack.
>
> On Thu, Jun 14, 2018, 4:20 PM Petr Pudlák <petr.mvd at gmail.com> wrote:
>
>> Hi everyone,
>>
>> I'd like to better understand the principles behind the 'size' parameter.
>> Looking at quickCheckWithResult [1], its computation seems to be somewhat
>> non-trivial, or even arbitrary. As far as I understand it, the size is
>> varied throughout tests, increasing from small to larger values. I see two
>> main purposes:
>>
>> - Test on smaller as well as larger values. But with generators having
>> proper distribution of values, this should happen anyway, just as if we had
>> a constant, larger 'size' parameter.
>> - Starting with smaller sizes allows to find smaller count-examples
>> first. But with shrinking, it doesn't matter that much, big
>> counter-examples are shrunk to smaller ones anyway in most cases.
>>
>> So is this parameter actually necessary? Would anything change
>> considerably if it was dropped?
>>
>> Thanks,
>> Petr
>>
>> [1]
>> http://hackage.haskell.org/package/QuickCheck-2.11.3/docs/src/Test-QuickCheck-Test.html#quickCheckWithResult
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