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? btw: These are two examples i looked at in hackage: Data.Complex.Complex (which is special, cause it is mathematically defined, what (*), abs, signum and fromInteger should do (i think)) and Physics.Hipmunk.Common.Vector (http://hackage.haskell.org/packages/archive/Hipmunk/5.0.0/doc/html/Physics- Hipmunk-Common.html#9) Sönke