On Mon, Aug 18, 2003 at 07:33:47PM +0200, Konrad Hinsen wrote:
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.
Would this suffice? module Foo where class Vect v a | v -> a where (<+>), (<->) :: Floating a => v -> v -> v (<*>) :: Floating a => a -> v -> v data Vector a = Vector a a a deriving (Show) instance Vect (Vector a) a where (<+>) = fzipWith (+) (<->) = fzipWith (-) (<*>) = fmap . (*) instance Vect [Vector a] a where (<+>) = zipWith (<+>) (<->) = zipWith (<->) (<*>) = fmap . (<*>) instance Functor Vector where fmap f (Vector x y z) = Vector (f x) (f y) (f z) class Functor z => Ziptor z where fzipWith :: (a -> b -> c) -> z a -> z b -> z c instance Ziptor Vector where fzipWith f (Vector x1 y1 z1) (Vector x2 y2 z2) = Vector (f x1 x2) (f y1 y2) (f z1 z2) Hm, did anyone else ever want a Ziptor class? (I didn't, until now ;)) Happy hacking, Remi -- Nobody can be exactly like me. Even I have trouble doing it.