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

[Magicloud Magiclouds]

Hum... simple like that. So you meant the Monoid just
abstracts/represents the ability to build a stack, right?

2009/11/14 Rafael Gustavo da Cunha Pereira Pinto <RafaelGCPP.Linux at gmail.com>:
> Disclaimer: I don't really know all about category theory, so some
> definitions might not be absolutely correct.
>
> Monoid is the category of all types that have a empty value and an append
> operation.
>
> The best example is a list.
>
> instance Monoid [a] where
>
>         mempty  = []
>         mappend = (++)
>
>
>
> Why do I need it? Well, you can think of a function where you need to
> incrementally store data.
>
> Storing them to a Monoid, you can start with a list and then change to a
> Set, without changing the function itself, because it would be defined based
> on the Monoid operations.
>
> instance Ord a => Monoid (Set a) where
>
>     mempty  = empty
>     mappend = union
>
>     mconcat = unions
>
> Hope I have helped!
>
> Regards,
>
> Rafael
>
>
>
> On Fri, Nov 13, 2009 at 14:14, Magicloud Magiclouds
> <magicloud.magiclouds at gmail.com> wrote:
>>
>> Hi,
>>  I have looked the concept of monoid and something related, but
>> still, I do not know why we use it?
>>
>> --
>> 竹密岂妨流水过
>> 山高哪阻野云飞
>>
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>>
>
>
>
> --
> Rafael Gustavo da Cunha Pereira Pinto
>
>



-- 
竹密岂妨流水过
山高哪阻野云飞