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List:       haskell-cafe
Subject:    [Haskell-cafe] Re: what is inverse of mzero and return?
From:       Ashley Yakeley <ashley () semantic ! org>
Date:       2005-01-25 11:37:12
Message-ID: ashley-2D4CA3.03371225012005 () sea ! gmane ! org
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In article <41F62049.4010403@imperial.ac.uk>,
 Keean Schupke <k.schupke@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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