On Sat, Jan 17, 2009 at 4:32 PM, Jeff Wheeler <j...@nokrev.com> wrote: > On Sat, 2009-01-17 at 21:55 +0100, Jean-Philippe Bernardy wrote: > >> I think it should admit empty, and the traversable instance should >> traverse the first list in reverse. > > I fixed the latter issue so that the behavior is correct (I think).
That's correct, but I think you'd be better off defining OpApplicative (or Backward, as I call it) locally and avoiding the two reverses. > I'm undecided about allowing them to be empty. I don't know the theory > or math behind zippers (I'm sure there are some papers written about > it), but it doesn't make much sense to be empty. I got that impression > from #haskell, also. If you look at a zipper as a list with a selected element, then it doesn't make sense to talk about a zipper of an empty list. That being said, I'd prefer fromList to have the type [a] -> Maybe (Zipper a), and similarly with next and previous. If people want to live dangerously, they can use fromJust. -- Dave Menendez <d...@zednenem.com> <http://www.eyrie.org/~zednenem/> _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
