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