Re: [Haskell-cafe] Re: Coarbitrary

On Thu, 27 Oct 2005, Shae Matijs Erisson wrote:

Joel Reymont writes:

...

I could not understand how to define this for arbitraries of my choosing and Shae seems to have defined coarbitrary = error "Not implemented" :-).

Coarbitrary is for generator transformers, see section 3.3 on page 5 of the original paper http://www.md.chalmers.se/~koen/Papers/quick.ps

You need coarbitrary for Word32 if you want to generate arbitrary functions of type Word32 -> <something>. As you will see in the QuickCheck paper Coarbitrary instances can (often) be defined mechanically. I think QuickCheck 2 includes default coarbitrary methods implemented using generic classes (http://haskell.org/ghc/docs/latest/html/users_guide/generic-classes.html). -- /NAD