Hussein,
How are you constructing your zipper, before passing it to traverse?
Note that clojure.zip doesn't work on arbitrary data structures
without being given some information about how to descend
into/construct nodes, etc. - i.e. z/next expects a zipper, and your
data structure isn't a zipper, but an input to a zipper. Unless
you've written a zipper you omitted from your post, zipping over maps,
in particular, may not be as convenient as you're imagining.
https://clojuredocs.org/clojure.zip/zipper has helpful examples in it.
Take care,
Moe
On Fri, Aug 21, 2015 at 5:06 PM, Hussein B. <hubaghd...@gmail.com> wrote:
> Hi,
>
> I changed println to z/node , this time I'm getting:
>
> NullPointerException clojure.zip/branch? (zip.clj:73)
>
> On Friday, August 21, 2015 at 5:56:10 PM UTC+2, Moe Aboulkheir wrote:
>>
>> Hussein,
>>
>> The println inside (recur) will return nil.
>>
>> Take care,
>> Moe
>>
>> On Fri, Aug 21, 2015 at 4:35 PM, Hussein B. <hubag...@gmail.com> wrote:
>> > Hi,
>> >
>> > I have this structure:
>> >
>> > (def s [{"n" {"id" "a"} "d" 2 "children" [{"n" {"id" "c"} "d" 4
>> > "children"
>> > []}]} {"n" {"id" "b"} "d" 3 "children" []}])
>> >
>> >
>> >
>> > And I wrote a function with zippers to traverse it:
>> >
>> > (defn traverse [col]
>> > (loop [z col]
>> > (if (= (z/next z) z)
>> > z
>> > (if (z/branch? z)
>> > (recur (z/next z))
>> > (recur (-> z println z/next))))))
>> >
>> >
>> > But I'm getting: NullPointerException clojure.zip/next (zip.clj:236)
>> >
>> > Any ideas?
>> >
>> > Thanks for help.
>> >
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