[Haskell-cafe] Category Theory woes

Nick Rudnick joerg.rudnick at t-online.de
Wed Feb 17 22:27:31 EST 2010

I haven't seen anybody mentioning «Joy of Cats» by  Adámek, Herrlich & 

It is available online, and is very well-equipped with thorough 
explanations, examples, exercises & funny illustrations, I would say 
best of university lecture style: http://katmat.math.uni-bremen.de/acc/. 
(Actually, the name of the book is a joke on the set theorists' book 
«Joy of Set», which again is a joke on «Joy of Sex», which I once found 
in my parents' bookshelf... ;-))

Another alternative: Personally, I had difficulties with the somewhat 
arbitrary terminology, at times a hindrance to intuitive understanding - 
and found intuitive access by programming examples, and the book was 
«Computational Category Theory» by Rydeheart & Burstall, also now 
available online at http://www.cs.man.ac.uk/~david/categories/book/, 
done with the functional language ML. Later I translated parts of it to 
Haskell which was great fun, and the books content is more beginner 
level than any other book I've seen yet.

The is also a programming language project dedicated to category theory, 
«Charity», at the university of Calgary: 

Any volunteers in doing a RENAME REFACTORING of category theory together 
with me?? ;-))



Mark Spezzano wrote:
> Hi all,
> I'm trying to learn Haskell and have come across Monads. I kind of understand monads now, but I would really like to understand where they come from. So I got a copy of Barr and Well's Category Theory for Computing Science Third Edition, but the book has really left me dumbfounded. It's a good book. But I'm just having trouble with the proofs in Chapter 1--let alone reading the rest of the text. 
> Are there any references to things like "Hom Sets" and "Hom Functions" in the literature somewhere and how to use them? The only book I know that uses them is this one. 
> Has anyone else found it frustratingly difficult to find details on easy-to-diget material on Category theory. The Chapter that I'm stuck on is actually labelled Preliminaries and so I reason that if I can't do this, then there's not much hope for me understanding the rest of the book...
> Maybe there are books on Discrete maths or Algebra or Set Theory that deal more with Hom Sets and Hom Functions?
> Thanks,
> Mark Spezzano.
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