[Haskell-cafe] Could someone teach me why we use Data.Monoid?

Magnus Therning magnus at therning.org
Fri Nov 13 16:53:43 EST 2009

On 13/11/09 18:43, Edward Kmett wrote:
> Watch out, in more common parlance, having just an binary operation is a
> magma, while having a category with full inverses yields a groupoid. I
> haven't seen many people use the older groupoid term for magmas, if only
> because they started to have naming conflicts with the category theory
> people, and Bourbaki's 'magma' was available and unambiguous. =)
> And of course magma is not to be confused with the notion of a
> semigroup, which is a binary associative operation, and is therefore
> much more similar to a monoid in that all it lacks is a unit.

I suspect there'll be some bald (evil) haskeller out there filing a bug report
right now for the type class Magma (with the alias LiquidHotMagma of course).
Using it will require programming with just one hand though, since one pinkie
must be between one's teeth.


Magnus Therning                        (OpenPGP: 0xAB4DFBA4)
magnus@therning.org          Jabber: magnus@therning.org
http://therning.org/magnus         identi.ca|twitter: magthe

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