This traverses the list three times (reverse, init and last are each linear time): fromListEnd xs = Zipper (reverse $ init xs) (last xs) []
But we only need to do it once: fromListEnd xs = let x:xs' = reverse xs in Zipper xs' x [] I don't *think* this has an effect on strictness/laziness, since both versions are strict in the spine of the list. --Max On Sat, Jan 17, 2009 at 10:33 AM, Jeff Wheeler <j...@nokrev.com> wrote: > Hi, > > (I also sent this to libraries@, but without response; I'm posting here > for a wider audience.) > > I'm somewhat of a beginner in Haskell, so take what I say with a grain > of salt, please. > > The ListZipper implementation seems very odd to me, and #haskell seemed > to agree with me. The current package implements a Zipper with > >> data Zipper = Zipper ![a] ![a] > > which allows for empty zippers, among other things. Very strange to me. > It also seems unnecessarily strict. There are also no expected > typeclasses implemented, like Foldable or Traversable. > > I thought it would be interesting to try fixing these problems with a > much cleaner design, and I'd like to share what I came up with: > > http://hpaste.org/14030 > > I'd very much appreciate some criticism of the code so that I can > improve it. > > I'm not sure how best to provide this alternative on Hackage; should we > make this merely a newer version of the old library, provide it in a > conflicting package, or find a new namespace for it and provide it > there? > > Thanks, > > Jeff Wheeler > > _______________________________________________ > Haskell mailing list > Haskell@haskell.org > http://www.haskell.org/mailman/listinfo/haskell > _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
