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

[Oleg Grenrus]

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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