On Monday 18 August 2003 19:10, Andre Pang wrote:
This seems to work (with -fglasgow-exts):
module Foo where
class Vect v where (<+>) :: v -> v -> v
data Vector a = Vector a a a deriving (Show, Eq)
instance Floating a => Vect (Vector a) where (<+>) (Vector x1 y1 z1) (Vector x2 y2 z2) = Vector (x1+x2) (y1+y2) (z1+z2)
instance Floating a => Vect [Vector a] where (<+>) l1 l2 = zipWith (<+>) l1 l2
*Foo> (Vector 5 6 7) <+> (Vector 1 2 3) Vector 6.0 8.0 10.0 *Foo> [Vector 1 2 3, Vector 10 20 30] <+> [Vector 100 200 300, Vector 4 5 6] [Vector 101.0 202.0 303.0,Vector 14.0 25.0 36.0]
... or does example not do something which you want it to do?
Well, yes, because my original example was cut down to illustrate the problem I had. The full version of the class Vect is class Vect v a where (<+>) :: Floating a => v a -> v a -> v a (<->) :: Floating a => v a -> v a -> v a (<*>) :: Floating a => a -> v a -> v a I need the parametrization on a in order to be able to define the type of scalar multiplication. I do have the choice of "class Vect v" or "class Vect v a", both seem to do the same in this context, but in both cases "v" has the role of a type constructor. Konrad.