On Fri, 2009-01-23 at 22:58 +0000, Olex P wrote:
Well if telepaths on vacation...
class Vector v where (^+^) :: v -> v -> v
data Vector3 = V3 !Double !Double !Double
instance Vector Vector3 where (V3 x1 y1 z1) ^+^ (V3 x2 y2 z2) = V3 (x1 + x2) (y1 + y2) (z1 + z2)
class Matrix m where (^+^) :: m -> m -> m
data Matrix3 = M3 !Vector3 !Vector3 !Vector3
instance Matrix Matrix3 where
(M3 r11 r12 r13) ^+^ (M3 r21 r22 r23) = M3 (r11 ^+^ r21) (r12 ^+^ r22) (r13 ^+^ r23)
Hope this is better :) So yeah... r11 ^+^ r21 just doesn't work.
I think you mis-understand how classes work in Haskell. They aren't like classes in OO languages. They're a little bit like interfaces in OO languages, but here we see another difference: in OO, you know an object has a certain class, so you use that to find out what a method name means. In Haskell, it's the other way around: you know a method belongs to a certain class, so you know its argument (or result) must come from an instance of that class. You can't re-use method names for multiple classes, though - you have to either use different names (e.g., div vs. (/) in Prelude) or use a common base class. jcc