[Haskell-cafe] [ANN] extended-categories

[Ian Milligan]

Hi John, amazingly I hadn't ran into this package. It seems that we take 
very different approaches to functors. I borrowed the 'data-category' 
approach of named functors, while hask uses the standard approach of 
implicit functors. Without explicit functors, there are many functors that 
we cannot express, such as the product functor or the diagonal functor. I 
will have to look at hask in more depth, however, I am sure there are many 
ideas I could borrow.

Ian

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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