type classes and generality
Mon, 09 Jul 2001 18:26:27 -0400
> On 09-Jul-2001, Norman Ramsey <email@example.com> wrote:
> > I'm trying to model probability and leave the
> > representation of probability unspecified other than
> > it must be class Real. But I'm having trouble with
> > random numbers; how can I show that if a type has class Real,
> > it also has class Random.Random? Is there a way to accomplish
> > this goal other than by changing the library?
> I'm not sure if I fully understand your goal.
> But one thing you can do is to define a wrapper type
> newtype WrapReal r = WrapReal r
> and make the wrapper an instance of Random.Random
> if the underlying type is an instance of Real
> instance Real r => Random.Random (WrapReal r) where
> Then you can use the wrapper type whenever you want to get a random number.
The problem is that without intensional type analysis, I wouldn't know
how to fill in the instance methods in the `...'