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

[Joe Fredette]

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  
> <ben.franksen at online.de> 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 <dave at zednenem.com>
> <http://www.eyrie.org/~zednenem/>
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