[Haskell-cafe] Relevance and applicability of category theory

[Gabor Greif]

Am 31.01.2008 um 01:23 schrieb aaltman at pdx.edu:

> 3. I believe the documentation stating that Haskell arrows are a  
> generalization of Haskell monads, but arrows are a categorical  
> thing too and in that context bear a much more distant relationship  
> to monads.  Does a Haskell arrow have Hask as domain and codomain?   
> Or is one particular element in Hask its domain and possibly  
> another its codomain?  Those are not at all the same thing.


Without being able to dive into this matter now,
I just want to say that both the Haskell monads
and arrows can be generalized to something
I call a "thrist", which appears to be the moral
equivalent of a free category. The underlying
category is obtained by a two-parameter GADT
(defining the morphisms) and the domains and
codomains of its members (which are Haskell types)
being the objects.

Here is my blog entry that motivates the concept
a bit:

http://heisenbug.blogspot.com/2007/11/trendy-topics.html

Cheers,

	Gabor

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