Hrm. Sounds like getting the hash of an infinite sequence will hang or cause OOME.
On the one hand, *most* uses of the hash are followed by .equals if the hashes match, and .equals on an infinite seq can't work, since if it gives up and says "equal" after some large number N of elements, the seqs might still differ at position N + 1, and there's no *general* way to determine in an analytic manner whether two seqs will produce identical output, or even whether they're infinite (even given the generating code, those're equivalent to the halting problem). On the other hand, the above use of the hash does *not* require equals to work. Hash could be changed to use only the first N elements of the seq, at most, for some N, and would then work for such uses as in the generic .toString. On the gripping hand, a) doing this would make infinite seqs *mostly* work in associative data structures, but with intermittent failures (when there were collisions), instead of failing promptly every time, and b) .toString for LazySeq might more productively just produce "(the seq)", if it's going to fail on infinite seqs anyway. On Fri, Mar 22, 2013 at 2:29 AM, Nelson Morris <nmor...@nelsonmorris.net>wrote: > If I'm reading everything correctly: > > 1. Object 's .toString uses .hashCode() > 2. LazySeq 's .hashCode() uses seq() which realizes a seq. > 3. LazySeq 's .hashCode() calls .hashCode() on the realized seq > 3. (map ..) creates a LazySeq with a fn to create (cons val (lazy-seq > (map f rest))) > 4. (cons ... ...) creates a Cons > 5. Cons uses Aseq's .hashcode() which traverses each object in the seq > and merges the hashcodes together. > > A similar thing happens with a (range) as it builds a ChunkedCons > which also uses Aseq's hashcode. > > On Fri, Mar 22, 2013 at 12:53 AM, Marko Topolnik > <marko.topol...@gmail.com> wrote: > > I am deeply puzzled abouth the behavior of .toString invocation on a lazy > > sequence. > > > > ==> (.getClass (map println (range 100))) > > clojure.lang.LazySeq > > ==> (.toString (map println (range 100))) > > ;; integers 0..100 printed > > "clojure.lang.LazySeq@590b4b81" > > > > It should be obvious from the output, but for the record: LazySeq doesn't > > override toString, so just the basic Java method is called. How can this > > possibly cause the sequence to be realized? > > > > Beyond my curiosity, however, what possible purpose could such behavior > > serve? > > > > -marko > > > > > > > > On Thursday, March 21, 2013 7:54:39 PM UTC+1, Razvan Rotaru wrote: > >> > >> Hi, > >> > >> I'm curious, why doesn't toString of clojure.lang.LazySeq return the > >> entire sequence as a String, and returns the Java pointer instead? I > find it > >> annoying when I do this: > >> > >> > >> user> (str (map + [1 2 3])) > >> "clojure.lang.LazySeq@7861" > >> > >> > >> What's the reason behind this decision? Shouldn't toString trigger the > >> evaluation of the sequence? Doesn't it do that for other values, like > >> numbers and vectors? > >> > >> Is there an alternative to the code above (preferably simple and > elegant), > >> which will return the etire sequence? > >> > >> > >> Thanks, > >> Răzvan > > > > -- > > -- > > You received this message because you are subscribed to the Google > > Groups "Clojure" group. > > To post to this group, send email to clojure@googlegroups.com > > Note that posts from new members are moderated - please be patient with > your > > first post. > > To unsubscribe from this group, send email to > > clojure+unsubscr...@googlegroups.com > > For more options, visit this group at > > http://groups.google.com/group/clojure?hl=en > > --- > > You received this message because you are subscribed to the Google Groups > > "Clojure" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to clojure+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/groups/opt_out. > > > > > > -- > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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