[Haskell-cafe] Num instances for 2-dimensional types

[Soenke Hahn]

On Monday 05 October 2009 10:14:02 pm Henning Thielemann wrote:
> Sönke Hahn schrieb:
> > Hi!
> >
> > I often stumble upon 2- (or 3-) dimensional numerical data types like
> >
> >     (Double, Double)
> >
> > or similar self defined ones. I like the idea of creating instances for
> > Num for these types. The meaning of (+), (-) and negate is clear and very
> > intuitive, i think. I don't feel sure about (*), abs, signum and
> > fromInteger. I used to implement
> >
> >     fromInteger n = (r, r) where r = fromInteger n
> >
> > , but thinking about it,
> >
> >     fromInteger n = (fromInteger n, 0)
> >
> > seems very reasonable, too.
> >
> > Any thoughts on that? How would you do it?
> 
> I use NumericPrelude that has more fine grained type classes. E.g. (+)
> is in Additive and (*) is in Ring.
> 
> http://hackage.haskell.org/package/numeric-prelude
> 

That is pretty cool, thanks. How do your import statements look like, when you 
use numeric-prelude? Mine look a bit ugly:

import Prelude hiding ((+), (-), negate)
import Algebra.Additive ((+), (-), negate)

Sönke