Ticket with patch at
http://dev.clojure.org/jira/browse/CLJ-1317
The problem is that seq-zip uses clojure.core/identity as the
"children" argument to zipper. Applied to (), this returns (), but
clojure.zip expects the "children" function to return nil when there
are no children. The patch attached to the ticket above changes
identity to seq inside seq-zip. This suffices to fix the behaviour
discovered by Lee.
Cheers,
Michał
On 1 January 2014 00:15, Lee Spector <lspec...@hampshire.edu> wrote:
>
> On Dec 31, 2013, at 5:08 PM, Armando Blancas wrote:
>
>> 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
>
> Does that mean that you think that the behavior is correct and expected?
>
> It goes down () thinking it can have children -- fine -- but when there
> aren't any children shouldn't zip/next continue until it hits the next thing?
> Why should it "land" on a non-existent nil instead?
>
> Compare:
>
> Traversing '((1) 0) with zip/next we get 4 items: ((1) 0), (1), 1, 0
>
> Traversing '(() 0) with zip/next we also get 4 items: (() 0), (), nil, 0
>
> It seems to me that these shouldn't both give 4 things, since the second
> clearly contain one less thing. That alleged nil just isn't there. Note also
> that:
>
> Traversing '((nil) 0)) with zip/next we also get 4 items: ((nil) 0), (nil),
> nil, 0
>
> That one seems right to me -- there really IS a nil there this time. But the
> one with () doesn't.
>
> If I'm alone in this then I guess I'll just write my own zip_really_next that
> does what I expect, but I'm curious if others also think that the current
> behavior is correct.
>
> Thanks,
>
> -Lee
>
>
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