On 26 Feb 2009, at 09:02, Daneel Yaitskov wrote:
-------------- But I can't instance my own class:
class (Num a) => SVect a where (***) :: Num b => a -> b -> a
instance (Num t) => SVect (Vertex3 t) where (Vertex3 x y z) *** c = Vertex3 (c*x) (c*y) (c*z)
GHC posts about the error:
surface.hs:107:36: Couldn't match expected type `b' against inferred type `t' `b' is a rigid type variable bound by the type signature for `***' at surface.hs:103:14 `t' is a rigid type variable bound by the instance declaration at surface.hs:105:14 In the second argument of `(*)', namely `x' In the first argument of `Vertex3', namely `(c * x)' In the expression: Vertex3 (c * x) (c * y) (c * z) ------------------------
I understand the "c" argument must have type as x,y and z, but I don't know what need to do.
I don't immediately see what is causing your error, but try downloading the VectorSpace package off hackage – it may save you a lot of wheel reinventing here. Bob