perhaps

[Benjamin Franksen]

ajb at spamcop.net wrote:
> Slightly contradicting myself, here's one that I use:
> 
>     class TestableProperty prop a | prop -> a where
>         is :: prop -> a -> Bool
> 
>     data Prime = Prime
> 
>     instance TestableProperty Prime Integer where
>         is Prime x = {- detail omitted -}
> 
> The only problem with this is that with the fundep, you can't do this:
> 
>     instance (Integral i) => TestableProperty Prime i where
>         is Prime x = {- same detail -}

Maybe I'm dense but couldn't you just drop the fundep?

Cheers,
Ben