The implementation of seq-zip uses seq? as its branching predicate. As a
result the zipper goes down on () thinking it can have children:
user=> (seq? ())
true
user=> (seq? {})
false
user=> (seq? #{})
false
user=> (seq? [])
false
On Sunday, December 29, 2013 10:14:23 AM UTC-8, Lee wrote:
>
>
> I realize that many people are on holiday, but I'm hoping to get some
> clarity about how to proceed with respect to this issue in the near future.
>
> Can anyone tell if I'm right that this is a bug in clojure.zip? If so,
> then is the right thing to do to post an issue on JIRA?
>
> I've re-included the crux of the issue [slightly edited and recombined]
> below.
>
> Thanks,
>
> -Lee
>
>
> On Dec 21, 2013, at 11:49 AM, Lee Spector wrote:
> > When I step through a zipper made from a nested list via seq-zip, I get
> extraneous nils after processing a nested ().
> >
> > Is this somehow expected behavior, or a bug, or am I misunderstanding
> something fundamental?
> >
> > The problem seems to arise only when an nested empty list is present,
> not other nested lists [... deleted ...]
> >
> > Here's an illustration, stepping through '(() 0) with next and printing
> the node at each step:
> >
> > (loop [z (zip/seq-zip '(() 0))]
> > (if (zip/end? z)
> > :done
> > (do (println (zip/node z))
> > (recur (zip/next z)))))
> >
> > That produces:
> >
> > (() 0)
> > ()
> > nil
> > 0
> > :done
> >
> > I don't expect the nil to be there.
>
> > [That is,] when traversing '(() 0) with zip/next, one should first visit
> the root, then (), and then 0. But what actually happens is that between
> then () and the 0 one lands on a non-existent nil node. So one ends up
> visiting 4 nodes when there are only 3, and the extra one is a nil.
>
>
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