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).
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). Perhaps this is why (intersection) is not supported at this time, even though (union) returns an empty set object, the identity element for the union operation. On Fri, Jan 24, 2014 at 3:34 PM, Jarrod Swart <jcsw...@gmail.com> wrote: > Ah cool, thanks for posting your solution! > > On Friday, January 24, 2014 3:29:49 PM UTC-5, Tassilo Horn wrote: > >> Jarrod Swart <jcs...@gmail.com> writes: >> >> > The reason you can't get this to work is that r/map returns a >> <reducible> >> > not a <coll> for reduce to operate on. >> >> Ah, indeed. I couldn't see the forest for the trees. >> >> > I'm not sure of a solution because I'm not familiar with >> > core.reducers. >> >> This works: >> >> (reduce set/intersection (r/foldcat (r/map set [[1 2] [3 1] [1 3]]))) >> >> Bye, >> Tassilo >> > -- > -- > 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.
