You need to write an instance of the Num class, eg instance Num Quaternion where (Q a b c d) + (Q e f g h) = ... (Q a b c d) * (Q e f g h) = ... etc This allows Haskell to overload things like numbers. You seem to be headed in the right direction w/ your type signature, except (*) has type Num a => a -> a -> a Which means "For any type `a` that is an instance of the type class `Num`, this is a closed binary function on that type" HTH /Joe On Sep 9, 2009, at 4:51 PM, Amy de Buitléir wrote:
I'm trying to define a Quaternion, which is sort of a four-element vector with special rules for multiplication.
----- Quaternion.hs ----- data Quaternion = Quaternion Double Double Double Double deriving (Show)
(*) :: (Quaternion a) => a -> a -> a (*) (Quaternion w1 x1 y1 z1) (Quaternion w2 x2 y2 z2) = Quaternion w x y z where w = w1*w2 - x1*x2 - y1*y2 - z1*z2 x = x1*w2 + w1*x2 + y1*z2 - z1*y2 y = w1*y2 - x1*z2 + y1*w2 + z1*x2 z = w1*z2 + x1*y2 - y1*x2 + z1*w2
----- end code -----
When I try to load this into ghci, I get:
Quaternion.hs:6:13: Ambiguous occurrence `*' It could refer to either `Main.*', defined at Quaternion.hs:5:0 or `Prelude.*', imported from Prelude
... and lots more messages like that. I understand roughly what the message means, but I don't know how to tell it that when I use "*" within the definition, I just want ordinary multiplication. Thanks in advance for any help!
Amy
_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners