moved to haskell-cafe Ketil> E.g. way back, I wrote a simple differential equation solver. Ketil> Now, the same function *could* have been applied to vector Ketil> functions, except that I'd have to decide on how to implement Ketil> all the "Num" stuff that really didn't fit well. Ideally, a Ketil> nice class design would infer, or at least allow me to Ketil> specify, the mathematical constraints inherent in an Ketil> algorithm, and let my implementation work with any data Ketil> satisfying those constraints. the problem is that the --majority, I suppose?-- of mathematicians tend to overload operators. They use "*" for matrix-matrix multiplication as well as for matrix-vector multiplication etc. Therefore, a quick solution that implements groups, monoids, Abelian groups, rings, Euclidean rings, fields, etc. will not be sufficient. I don't think that it is acceptable for a language like Haskell to permit the user to overload predefined operators, like "*". A cheap solution could be to define a type MathObject and operators like :*: MathObject -> MathObject -> MathObject Then, the user can implement: a :*: b = case (a,b) of (Matrix x, Matrix y) -> foo (Matrix x, Vector y) -> bar -- Christoph Herrmann E-mail: herrmann@fmi.uni-passau.de WWW: http://brahms.fmi.uni-passau.de/cl/staff/herrmann.html