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

Stephen Tetley wrote:

2009/11/13 Rafael Gustavo da Cunha Pereira Pinto :

...

Monoid is the category of all types that have a empty value and an append operation.

Or more generally a neutral element and an associative operation:

The multiplication monoid (1,*)

9*1*1*1 = 9

1 is neutral but you might be hard pressed to consider it _empty_.

This is the thing. If we had a class specifically for containers, that could be useful. If we had a class specifically for algebras, that could be useful. But a class that represents "any possible thing that can technically be considered a monoid" seems so absurdly general as to be almost useless. If you don't know what an operator *does*, being able to abstract over it isn't especially helpful... ...in my humble opinion. (Which, obviously, nobody else will agree with.)