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

[Keean Schupke]

Ashley Yakeley wrote:

>In article <41F211FB.3030706 at imperial.ac.uk>,
> Keean Schupke <k.schupke at imperial.ac.uk> wrote:
>
>  
>
>>This fits the above description, but I don't see how the following can 
>>be true:
>>
>>    (mplus a b) >>= c = mplus (a >>= c) (b >>= c)
>>    
>>
>
>Try it (and my test code) with [], which is an instance of MonadPlus. 
>mplus is defined as (++) for [].
>
>  
>
but what if (a >>= c) causes c to fail, and (b >>= c) lets c succeed. In 
this
case the LHS will fail, whereas the RHS will succeed I think?
 
    Keean.