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.
