[Haskell-cafe] Very freaky

Alexis Hazell dry.green.tea at gmail.com
Thu Jul 12 05:27:44 EDT 2007

On Thursday 12 July 2007 04:40, Andrew Coppin wrote:

> I once sat down and tried to read about Category Theory. I got almost
> nowhere though; I cannot for the life of my figure out how the
> definition of "category" is actually different from the definition of
> "set". Or how a "functor" is any different than a "function". Or...
> actually, none of it made sense.


"Set" is just one type of category; and the morphisms of the category "Set" 
are indeed functions. But morphisms in other categories need not be 
functions; in the category "Rel", for example, the morphisms are not 
functions but binary relations.

A "functor" is something that maps functions in one category to functions in 
another category. In other words, functors point from one or more functions 
in one category to the equivalent functions in another category. Perhaps they 
could be regarded as 'meta-functions'.

Hope that helps,


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