On Mon, 13 Oct 2003 11:37:43 -0400 Jan-Willem Maessen <[EMAIL PROTECTED]> wrote:
> > So, the existential quantification permits more nuanced > > transformations -- and yet the nuances aren't observable. So, they > > don't matter? > > Whether they matter or not depends upon our aims. I'm curious about > what's possible---in the hopes that I can get a better handle on > what's really desirable in a particular situation. Indeed. One of the issues is useability or at least naturality. It seems that existentials in some situations better achieve the intent/goal. Anyways, if another challenge is desired, I would be interested in seeing how one would go about converting the implementation of Dynamics in "A Lightweight Implementation of Generics and Dynamics" into a form that doesn't use existentials* but still provides the same (or very similar or I guess simpler) interface. * No coding existentials as universals :P data Showable = Showable (forall r.(forall a.Show a => a -> r) -> r) mapM_ (\(Showable v) -> v print) [Showable ($ 5),Showable ($ True)] 5 True _______________________________________________ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
