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

A ring is an abelian group in addition, with the added operation (*) being distributive over addition, and 0 annihilating under multiplication. (*) is also associative. Rings don't necessarily need _multiplicative_ id, only _additive_ id. Sometimes Rings w/o ID is called a Rng (a bit of a pun). /Joe On Oct 7, 2009, at 4:41 PM, David Menendez wrote:

On Wed, Oct 7, 2009 at 12:08 PM, Ben Franksen wrote:

...

More generally, any ring with multiplicative unit (let's call it 'one') will do.

Isn't that every ring? As I understand it, the multiplication in a ring is required to form a monoid.

-- Dave Menendez http://www.eyrie.org/~zednenem/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe