RE: PolyKinds, Control.Category and GHC 7.6.1
| FWIW PolyKinds in 7.4 is rough, and I had experiences where enabling it | led to compile failures in downstream modules, so this wouldn't | necessarily have been painless. Hopefully with 7.6 it will be. PolyKinds is not an advertised feature of 7.4, so you should absolutely not rely on it working in 7.4. But it IS an advertised feature for 7.6 and should work flawlessly. (If not, yell.) Simon ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
PolyKinds, Control.Category and GHC 7.6.1
Would it be possible to add something like
{-# LANGUAGE CPP #-}
#if defined(__GLASGOW_HASKELL__) __GLASGOW_HASKELL__ = 704
{-# LANGUAGE PolyKinds #-}
#endif
to the top of Control.Category before the 7.6.1 final release?
Control.Category.Category is pretty much the only type in base that
directly benefits from PolyKinds without any code changes, but without
enabling the extension there nobody can define categories for kinds other
than *, and most interesting categories actually have more exotic kinds.
I only noticed that it wasn't there in the release candidate just now.
-Edward Kmett
___
Glasgow-haskell-users mailing list
Glasgow-haskell-users@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: PolyKinds, Control.Category and GHC 7.6.1
Control.Category.Category is pretty much the only type in base that directly benefits from PolyKinds without any code changes, but without enabling the extension there nobody can define categories for kinds other than *, and most interesting categories actually have more exotic kinds. What, precisely, is the benefit of turning on PolyKinds for that file without changing the code? If we're cpp'ing it in, then are there further benefits that we could also reap by cpp'ing some code changes? -- Dan Burton ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: PolyKinds, Control.Category and GHC 7.6.1
On Mon, Aug 13, 2012 at 9:55 AM, Dan Burton danburton.em...@gmail.comwrote: Control.Category.Category is pretty much the only type in base that directly benefits from PolyKinds without any code changes, but without enabling the extension there nobody can define categories for kinds other than *, and most interesting categories actually have more exotic kinds. What, precisely, is the benefit of turning on PolyKinds for that file without changing the code? If we're cpp'ing it in, then are there further benefits that we could also reap by cpp'ing some code changes? The benefit is that the kind of Category changes to Category :: (x - x - *) - Constraint This means I can do things like make data Dict p where Dict :: p = Dict p newtype a |- b = Sub (a = Dict b) and then (|-) :: Constraint - Constraint - * is a valid candidate to become a Category. Moreover, PolyKinds + DataKinds finally enable us to write product and sum categories, make categories for natural transformations, and generally finally put Category to work. These were all disallowed by the previous simpler kind. No code changes need be applied beyond permitting the type of Category to generalize and existing code continues to work. This change actually could have been applied in 7.4.1. -Edward Kmett ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
