I believe the documentation is imprecise as you point out. The "loc"
returned by next at the :end, is not a location as it lacks meta data. I
don't think this is intentional, but clearly I could be wrong.
I don't see any immediate issues in patching next like below so it returns
a real loc, and this would make your code work.
(defn next
...
(loop [p loc]
(if (up p)
(or (right (up p)) (recur (up p)))
(with-meta [(node p) :end] (meta loc)))))))
On Monday, December 2, 2013 6:01:06 PM UTC+1, Milton Silva wrote:
>
> I was trying to write a function next-branch.
>
> I wrote somthing like:
> (use 'clojure.zip)
> (def zp (seq-zip '(+ 1 2 (+ 3 4) (+ 5 6))))
> (defn next-branch [loc] (second (filter branch? (iterate next loc))))
>
> (next-branch (next-branch (next-branch zp)))
> this results in: NullPointerException clojure.zip/branch? (zip.clj:73)
>
> Reading the docs of next "returns a distinguished loc", this seams to
> imply next should always return a loc even when at the end. The docs of
> branch? "Returns true if the node at loc is a branch" seam to imply any
> loc will do.
>
> So this would lead me to concluded that next always returns a "loc" and
> since branch? is supposed to take a "loc" it should work.
>
> Why doesn't next return a loc at the end? Looking at the code I know "why"
> but is it intended to be this way? If so why?
>
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