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

Ashley Yakeley ashley at semantic.org
Tue Jan 25 06:37:12 EST 2005

In article <41F62049.4010403 at imperial.ac.uk>,
 Keean Schupke <k.schupke at imperial.ac.uk> wrote:

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

Every morphism in any category has a "from" object and a "to" object: it 
is a morphism from object to object. In the "Haskell category", a 
function of type 'A -> B' is a morphism from object (type) A to object B.

But in category theory, just because two morphisms are both from object 
A to object B does not mean that they are the same morphism. And so it 
is for the Haskell category: two functions may both have type 'A -> B' 
without being the same function.

Ashley Yakeley, Seattle WA

More information about the Haskell-Cafe mailing list