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

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 napsal:

Not only avoid extremely large trees, but in general guarantee termination of the generation process

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On 15 Jun 2018, at 0.31, David Feuer 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 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-QuickChec... _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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