[Haskell-cafe] Re: what is inverse of mzero and return?

[Jorge Adriano Aires]

> I think it would be helpful if all these classes came with their laws
> prominently attached in their Haddock documentation or wherever. 
Agree.

> The  trouble with MonadPlus is that the precise set of associated laws is
> either unspecified or not the most useful (I assume there's a paper on
> the class somewhere). I think everyone can agree on these:
>
>   mplus mzero a = a
>   mplus a mzero = a
>   mplus (mplus a b) c = mplus a (mplus b c)
<snip>
>   (mplus a b) >>= c = mplus (a >>= c) (b >>= c)

I just checked the paper,
"A monadic Interpretation of Tatics", by Andrew Martin and Jeremy Gibbons
http://web.comlab.ox.ac.uk/oucl/work/jeremy.gibbons/publications/tactics.pdf

And in deed, these are the listed laws for MonadPlus. On the other hand, Maybe 
is said to be an instance of MonadPlus.

So now I'm lost. 

Cheers,
J.A.