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
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