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

[Jorge Adriano Aires]

> But only some instances (such as []) satisfy this:
>
>   (mplus a b) >>= c = mplus (a >>= c) (b >>= c)
>
> Other instances (IO, Maybe) satisfy this:
>
>   mplus (return a) b = return a
>
> I think mplus should be separated into two functions. 

How would we implement the first kind in the Maybe instance of MonadPlus?

J.A.