On Feb 17, 10:54 am, Michael Gardner <gardne...@gmail.com> wrote: > On Feb 17, 2012, at 12:32 PM, Bill Smith wrote: > > > It might help to know that (= (range) (range)) does not terminate either. > > Of course, since a pairwise sequential comparison (what I assume is going on > under the hood) will never find a non-matching pair. > > > It appears that the = operator wants to fully evaluate the second argument > > before comparing to the first. Since (range) is infinite, it hangs. > > Yes, that is what appears to be happening. The question is: why? Why does it > only do this to the second argument? Why does (= v s) for any vector `v' and > any infinite lazy sequence `s' not terminate, while (= s v) does?
Lazy sequences implement java.util.List, which has a .size method. clojure.lang.APersistentVector/doEquiv (and doEquals) attempts to optimize when it sees it is being compared to something with a .size or .count method, by comparing sizes before doing the hard work of comparing elements. But this is not much of an optimization when the .size method is infinitely slow! Perhaps an additional test for lazy sequences should be added to these methods, but I'm certain the issue is more complicated than it appears after my cursory exploration, so that may well have other issues. -- 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
