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 and not other nested empty sequences (see example at bottom for
this bit).
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.
If I do this with a 1 in place of the () then it works as I expect:
(loop [z (zip/seq-zip '(1 0))]
(if (zip/end? z)
:done
(do (println (zip/node z))
(recur (zip/next z)))))
produces:
(1 0)
1
0
:done
It also works as I expect if I put (1) in place of (), suggesting that it's not
a problem with stepping over nested lists in general, but just with stepping
over ():
(loop [z (zip/seq-zip '((1) 0))]
(if (zip/end? z)
:done
(do (println (zip/node z))
(recur (zip/next z)))))
produces:
((1) 0)
(1)
1
0
:done
However, if I use non-list sequences then things seem to work as I would expect:
(loop [z (zip/seq-zip (seq [[] 0]))]
(if (zip/end? z)
:done
(do (println (zip/node z))
(recur (zip/next z)))))
produces:
([] 0)
[]
0
:done
This is with Clojure 1.5.1.
It's leading to null pointer exceptions in my application, so any explanations
or fixes or pointers would be very much appreciated.
Thanks,
-Lee
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