On Fri, Jan 24, 2014 at 12:56 PM, Cedric Greevey <cgree...@gmail.com> wrote:
> An interesting question this raises is if there is any sensible way to > define (intersection). It would need to behave as an identity element for > intersection, so would need to behave as a set (so, (set? (intersection)) > => truthy) that contained everything (so, (contains? (intersection) foo) => > foo no matter what foo is; (partial contains? (intersection)) => identity). > The problem would be what to do with seq? Ideally an infinite seq that will > produce any particular value after finite time would be produced, but > there's no way to sensibly produce "any particular value" given the wide > variety of constructor semantics, builders, factory methods, things not > known to this particular runtime instance but that conceptually exist > somewhere, etc.; of course, the seq return is a dummy of sorts anyway since > you couldn't really use it sensibly to it might as well just return > (range). Printing should likely be overridden to just print > "(intersection)" rather than b0rk the REPL with a neverending stream of > integers (or whatever). > Why should printing be overridden? If I print (range) I don't get "(range)". Also, contains? returns true if the first argument contains the second, not the second; (partial contains? (intersection)) => (constantly true). > But then it also subtly violates another property of Clojure set objects: > if (= a b), (not (identical? a b)), and (identical? (a-set a) a), then > (identical? (a-set b) a) and thus (not (identical? (a-set b) b)). The > latter is true under the hypothesis for every "real" set but would be false > for (intersection). > Is this a real property of Clojure's sets or an artifact of their present implementation? Is it something that anything impleneting IPersistentSet has to promise to uphold? -- Ben Wolfson "Human kind has used its intelligence to vary the flavour of drinks, which may be sweet, aromatic, fermented or spirit-based. ... Family and social life also offer numerous other occasions to consume drinks for pleasure." [Larousse, "Drink" entry] -- -- 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.
