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

19 Aug 2014

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Ian Milligan  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

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

John Wiegley