(take-nth 0 coll) redux...

Question

I dont seem to be able make the old ticket uninvalid so here goes
(take-nth 0 coll) causes (at least on Solaris) infinite space and time consumption
It's not a printout error as the following code causes the problem too

(let [j 0
 firstprod (apply * (doall (map #(- 1 %) (take-nth j (:props mix)))))]) ; from my parameter update function

I used jvisualvm and the jvm is doing some RNI call - no clojure code is running at all
If left alone it will crash the jvm with all heap space consumed
0 is an InvalidArgument for take-nth
I wouldnt mind if it produced an infinite lazy sequence of nils even though thats wrong
It doesnt do this though it actively destroys the JVM
Its a bug nasty destructive and it took me half a day to figure out what was going on
please let someone fix it!

Answer 1

Comment made by: importer

bhurt said: Before this bug gets marked as invalid as well, let me point out that the problem here is that (take-nth 0 any-list) is a meaningless construction- the only question is what to do when this happens. IMHO, the correct behavior is to throw an exception.

Answer 2

Comment made by: importer

ataggart said: (link: [file:dfNhoS2Cir3543eJe5cbLA)]: throws IllegalArgumentException on negative step size

Answer 3

Comment made by: importer

Converted from http://www.assembla.com/spaces/clojure/tickets/291
Attachments:
fixbug291.diff - https://www.assembla.com/spaces/clojure/documents/dfNhoS2Cir3543eJe5cbLA/download/dfNhoS2Cir3543eJe5cbLA

Answer 4

Comment made by: stu

Does calling (take-nth 0 ...) cause the problem, or only realizing the result?

Answer 5

Comment made by: chouser@n01se.net

I'm not seeing a problem. Calling take-nth and even partially consuming the seq it returns works fine for me:

(take 5 (take-nth 0 (link: 1 2 3)))
;=> (1 1 1 1 1)

Note however that it is returning an infinite lazy seq. The example in the issue description seems to include essentially (doall <infinite-lazy-seq>) which does blow the heap:

(doall (range))

This issue still strikes me as invalid.

Answer 6

Comment made by: richhickey

(take-nth 0 ...) returns an infinite sequence of the first item:

(take 12 (take-nth 0 (link: 1 2 3)))
=> (1 1 1 1 1 1 1 1 1 1 1 1)

Is something other than this happening on Solaris?

Answer 7

Reference: https://clojure.atlassian.net/browse/CLJ-291 (reported by alex+import)