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

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@imperial.ac.uk>, Keean Schupke 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.