instance Vector Vector2 where dot (V2 x1 y1) (V2 x2 y2) = x1 * x2 + y1 * y2
I tried to do something in CAL that I could not solve without functional dependencies. In their support forum, it got mentioned that func.deps propably won't make into the next Haskell standard... Any comments on
Amazing, so simple it is, Yoda would say ;) I did not realize one could perform "partial application" on types when declaring instances (I mean not specifying the type of Vector2 in <instance Vector Vector2>). Now regarding these funcdeps, are they "ill" as the "rumor" goes? Thanks, Peter -----Original Message----- From: Henning Thielemann [mailto:lemming@henning-thielemann.de] Sent: Thursday, July 12, 2007 11:44 AM To: peterv Cc: Haskell-Cafe@haskell.org Subject: Re: [Haskell-cafe] Functional dependencies *not* part of the next Haskell standard? On Thu, 12 Jul 2007, peterv wrote: that?
Now, the thing I tried to solve was:
data Vector2 a = Num a => V2 a a
class Vector a n | a -> n where dot :: a -> a -> n
instance Num a => Vector (Vector2 a) a where dot (V2 x1 y1) (V2 x2 y2) = x1 * x2 + y1 * y2
test1 = dot (V2 1.0 2.0) (V2 3.0 4.0)
class Vector v where dot :: Num a => v a -> v a -> a instance Vector Vector2 where dot (V2 x1 y1) (V2 x2 y2) = x1 * x2 + y1 * y2 This will work satisfyingly if you don't plan a larger type class hierarchy.