[Haskell-cafe] Very freaky

[Derek Elkins]

On Thu, 2007-07-12 at 14:07 -0700, Dan Piponi wrote:
> On 7/12/07, Andrew Coppin <andrewcoppin at btinternet.com> wrote:
> > Stefan O'Rear wrote:
> > > On Thu, Jul 12, 2007 at 07:19:07PM +0100, Andrew Coppin wrote:
> > >
> > >> I'm still puzzled as to what makes the other categories so magical that
> > >> they cannot be considered sets.
> 
> I thought I'd dive in with a comment to explain why category theory is
> an important subject and why it often crops up in Haskell programming.
> The key thing is this: in many branches of mathematics people draw
> what are known as commutative diagrams:
> http://mathworld.wolfram.com/CommutativeDiagram.html
> 
> So what do these diagrams represent? 

Equations.

> To a good approximation (and there is a certain amount of choice over
> which approximation you pick) Haskell also forms a category.

Haskell does form a category.  To a good approximation Haskell forms a
-nice- category.