[Haskell-cafe] lists as instances of a class?

[Henning Thielemann]

On Mon, 10 Jul 2006, David Roundy wrote:

> > class Vec v where
> >    (.+.) :: v -> v -> v
>
> > instance Vec [Double] where
> >    xs .+. ys = zipWith (+) xs ys
>
> > instance Vec Double where
> >    x .+. y = x + y
>
>
> P.S. This is with ghc 6.4.1.  And oddly enough, if you make the instance
>
> instance Num a => Vec [a] where
>    xs .+. ys = zipWith (+) xs ys

What about

instance Vec a => Vec [a] where
   (.+.) = zipWith (.+.)

?