[Haskell-cafe] Could someone teach me why we use Data.Monoid?
Rafael Gustavo da Cunha Pereira Pinto
RafaelGCPP.Linux at gmail.com
Fri Nov 13 12:16:47 EST 2009
*"...in my humble opinion. (Which, obviously, nobody else will agree with.)"
*
I somewhat agree with your opinion!!
What I miss the most is practical examples:
1) A function that uses a Monoid as a container
2) A function that uses Monoid as algebra
and so on, for most of categories.
I had a hard time understanding monads, not because I didn't understand the
concept of a monad, but because practical uses are missing, except on
Wadler's paper!
Regards
Rafael
On Fri, Nov 13, 2009 at 14:52, Andrew Coppin <andrewcoppin at btinternet.com>wrote:
> Stephen Tetley wrote:
>
>> 2009/11/13 Rafael Gustavo da Cunha Pereira Pinto <
>> RafaelGCPP.Linux at gmail.com>:
>>
>>
>>> 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.)
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
--
Rafael Gustavo da Cunha Pereira Pinto
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.haskell.org/pipermail/haskell-cafe/attachments/20091113/1227dc21/attachment.html
More information about the Haskell-Cafe
mailing list