On Tue, 21 Aug 2007, Peter Verswyvelen wrote:
Yes indeed, I realized that. I oversimplified my question. I'm basically trying to model 4D CG/HLSL operations (pixel/vertex shaders) in Haskell.
I tried realToFrac, but that did not work. Then I tried splitting the instances into Fractional and Integral, but I kept getting errors. Maybe because I also made the Vector datatype an instance of Num, Fractional, etc, which was needed to model the CG/HLSL piecewise operations (so multiplication of two vectors is done piecewise by default in the CG model; one has special dot, cross, and mul operations for performing the other operations).
It would be nice if one could have a full predicate in the constraints section of a type class, like
class ((Num a) && not (Vector4D a)) => ...
But I guess this indicates bad design?
Is still don't see why you need it. I have the feeling that you abuse Num and Fractional classes just for re-use of symbols like (*) and (/) in an arbitrary way. Better don't do that. Type classes are for writing generic functions. Define new infix operators where necessary.