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

[Keean Schupke]

I think I see, but if the objects are types, arn't the morphisms functions
on types not values?

    Keean.

Ashley Yakeley wrote:

>In article <41F61A0B.90005 at imperial.ac.uk>,
> Keean Schupke <k.schupke at imperial.ac.uk> wrote:
>
>  
>
>>I am sure monads in Haskell (and other functional languages like ML) are 
>>defined on types not values.
>>    
>>
>
>The objects of the category are types. The morphisms on the category are 
>functions. Two functions are the same if they match each value to the 
>same value. For the Functor laws and the Monad laws, the values 
>certainly do matter: if they didn't, they wouldn't correspond to the 
>category theory notions of functor and monad because the morphisms would 
>be wrong.
>
>  
>