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

Keean Schupke k.schupke at imperial.ac.uk
Mon Jan 24 13:18:31 EST 2005

Ashley Yakeley wrote:

>If you remember your category theory, you'll recall that two morphisms 
>are not necessarily the same just because they're between the same two 
>objects. For instance, the objects may be sets, and the morphisms may be 
>functions between sets: morphisms from A to B are the same only if they 
>map each element in A to the same element in B.
Yes, but I though the 'objects' in this case are endofunctors from a 
type to itself... the the morphisms operate on these endofunctors, the 
morphisms are unit and join.... such that joining 'unit' to the 
endofuntor retults in the endofunctor.

But I think that as the endofunctor is from the type to itself, the 
value does not
come into it.

    A -> A `join` unit  => A -> A


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