On Monday, August 18, 2003, at 04:56 PM, Konrad Hinsen wrote:
Continuing in my quest to understand type design in Haskell, here's another episode that leaves me scratching my head:
module Foo where
class Vect v a where (<+>) :: Floating a => v a -> v a -> v a
data Vector a = Vector a a a
instance Vect Vector a where (<+>) (Vector x1 y1 z1) (Vector x2 y2 z2) = Vector (x1+x2) (y1+y2) (z1+z2)
instance Vect [Vector a] a where (<+>) l1 l2 = zipWith (<+>) l1 l2
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? -- % Andre Pang : trust.in.love.to.save