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.li...@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.magiclo...@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 >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > > > -- > Rafael Gustavo da Cunha Pereira Pinto > > -- 竹密岂妨流水过 山高哪阻野云飞 _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
