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

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