Re: [Haskell-cafe] [ANN] extended-categories

19 Aug 2014


      I've now borrowed the approach of hask: an installation of an arrow is 
proof that its domain and codomain are objects. This is a great 
simplification.

On Tuesday, August 19, 2014 2:40:21 AM UTC-7, John Wiegley wrote:
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Ian Milligan javascript:> writes:
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extended-categories  is an 
implementation of categories designed to make use of GHC's recently 
enriched 
kind system. This project is a work in progress (only a few basic 
constructs 
are implemented), but your comments are welcomed. extended-categories 
requires a recent version of GHC (I have only tested it with 7.8.3).
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Categories are poly-kinded and have an Object constraint family:
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class Category m where 
    type Object (m :: k -> k -> *) (a :: k) :: Constraint 
    id :: Object m a => m a a 
    (.) :: (Object m a, Object m b, Object m c) => m b c -> m a b -> m a 
c
Hi Ian,
You should definitely also take a look at Edward Kmett's hask library:
https://github.com/ekmett/hask
He has taken the idea of poly-kinded Category and run with it in that 
library. 
To compare, he has:
class Category' (p :: i -> i -> *) where 
      type Ob p :: i -> Constraint 
      id :: Ob p a => p a a 
      observe :: p a b -> Dict (Ob p a, Ob p b) 
      (.) :: p b c -> p a b -> p a c
John 
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