[Haskell-cafe] [ANN] extended-categories

[Ian Milligan]

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:
>
> >>>>> Ian Milligan <ianm... at gmail.com <javascript:>> writes: 
>
> > extended-categories <github.com/ian-mi/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). 
>
> > Categories are poly-kinded and have an Object constraint family: 
>
> > 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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>
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