On Mon, 13 Oct 2003 11:37:43 -0400
Jan-Willem Maessen
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