Thanks Alex, If you ever do get a chance, I'd be curious to know what it was. The more I think about it the more I think Dan is correct. Also "scan" seems like a natural thing that one should be able to do without having to jump through hoops.
On Monday, February 29, 2016 at 5:10:53 PM UTC-5, Alex Miller wrote: > > I think that Rich had an objection to this, however in the haziness of > time I don't recall specifically what it was. If I get a chance, I will ask > him this week. > > On Monday, February 29, 2016 at 3:27:15 PM UTC-6, Patrick Curran wrote: >> >> Hi, >> >> I was trying to write a transducer and the 0-arity part of it never got >> called, which was unexpected. I did some searching and found this post: >> https://groups.google.com/forum/#!msg/clojure/uVKP4_0KMwQ/-oUJahvUarIJ. >> What Dan is proposing in that post would essentially solve my problem, but >> it doesn't look like his proposal has gotten much traction... >> >> Specifically I was trying to implement scan >> <http://reactivex.io/documentation/operators/scan.html>. >> >> (defn scan >> ([f] (scan f (f))) >> ([f init] >> (fn [xf] >> (let [state (volatile! init)] >> (fn >> ([] (xf (xf) init)) >> ([result] (xf result)) >> ([result input] >> (let [next-state (f @state input)] >> (vreset! state next-state) >> (xf result next-state)))))))) >> >> Which results in the following: >> (require '[clojure.core.reducers :as r]) >> (r/reduce ((scan + 3) conj) [1 2 3]) >> => [3 4 6 9] >> (transduce (scan + 3) conj [1 2 3]) >> => [4 6 9] >> (transduce (scan + 3) conj (((scan + 3) conj)) [1 2 3]) >> => [3 4 6 9] >> >> My expectation would be that we'd always get the 3 at the front of the >> vector. >> >> I'm actually using core.async and I'm expecting that the initial value be >> available to be taken from the channel. >> (require '[clojure.core.async :as a :include-macros true]) >> (def c (a/chan 1 (scan + 3))) >> (a/go (println (a/<! c))) >> ; expecting 3 to immediately be printed. >> (a/>!! c 1) >> => 4 >> >> So this is more of a conceptual thing rather than just how transduce is >> implemented. >> >> I'd love to hear other people's thoughts on this. I'm quite new, but >> Dan's proposal definitely feels "correct" and the current implementation >> definitely feels "wrong". >> >> --Patrick >> >> >> -- 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/d/optout.
