[QuickCheck] Bug with Small and Positive types

[Anders Persson]

The Arbitrary instance for Small does not use the arbitrary for the inner type. Instead it uses choose.
As a workaround you can switch the order of the modifiers:

>>> sample (arbitrary :: Gen (Positive (Small Int)))
Positive {getPositive = Small {getSmall = 1}}
Positive {getPositive = Small {getSmall = 3}}
Positive {getPositive = Small {getSmall = 2}}
Positive {getPositive = Small {getSmall = 3}}

/Anders

On 4 maj 2014, at 05:24, Bryan O'Sullivan <bos at serpentine.com> wrote:

> Not exactly expected behaviour: I get values that are not positive.
> 
> >>> sample (arbitrary :: Gen (Small (Positive Int)))
> Small {getSmall = Positive {getPositive = 0}}
> Small {getSmall = Positive {getPositive = -1}}
> Small {getSmall = Positive {getPositive = 2}}
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