This is still just recursion because of the map. That means it has all the
problems of recursion. If you need to avoid recursion, you need to do a
depth first or breadth first traversal of the tree and hold onto state as
you do it. The zipper does some of this for you and provides an easy way to
traverse data in a depth first fashion. If you need additional state, say
to collect data, or track data as you mutate the tree, then zip-visit may
or may not help.
Ultimately, to use a zipper you need to structure your algorithms to work
with a depth first traversal rather than using tree recursion. That said,
doing standard tree recursion may be the right answer. It all depends on
your use case.
On Wednesday, December 4, 2013 8:38:11 PM UTC-5, dabd wrote:
>
> Thanks I'll take a look at your libraries.
> One problem I found with the zipper API is that if you have a recursive
> function that takes a loc, when you call it on the clojure.zip/children of
> a given loc it won't work because this function returns a seq of nodes
> instead of a seq of locs. Shouldn't we add a function like
> children-as-locs to the API for this purpose or is there another way?
>
> (defn children-as-locs
> "Returns a seq of locs of the children of loc."
> [loc]
> (when (z/branch? loc)
> (let [[node path] loc
> cs (z/children loc)]
> (map-indexed (fn [i c]
> (with-meta [c {:l (vec (take i cs))
> :pnodes (if path (conj (:pnodes path)
> node) [node])
> :ppath path
> :r (vec (drop (inc i) cs))}]
> (meta loc)))
> cs))))
>
> On Wednesday, December 4, 2013 11:46:29 PM UTC, Alexander Hudek wrote:
>>
>> Additionally, if you need more complex access patterns you could see if
>> this helps:
>>
>> https://github.com/akhudek/zip-visit
>>
>> For performance, there is a fast-zip library that is api compatible with
>> clojure.zip. You can just swap the clojure.zip namespace for the fast-zip
>> namespace. Note that you'd need to make the same swap in any libraries you
>> use with your zippers (like zip-visit) since fast-zip is not implementation
>> compatible with clojure.zip.
>>
>> More broadly, I've found that straight up recursive algorithms can be a
>> lot faster than zippers, especially for read only operations. Of course the
>> stack size limits what you can do with tree recursion. As others have said,
>> it's best to see if you actually have performance problems first.
>>
>> On Wednesday, December 4, 2013 5:30:02 PM UTC-5, James Reeves wrote:
>>>
>>> On 4 December 2013 21:09, dabd <[email protected]> wrote:
>>>
>>>> I didn't get there because I ran into problems with the zipper API.
>>>> When you call 'children' on a loc you get a seq of nodes instead of a seq
>>>> of locs which causes me problems in a recursive algorithm operating on
>>>> locs.
>>>>
>>>
>>> Have you tried using next and end? for a depth-first transversal?
>>>
>>> - James
>>>
>>
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