This was discussed further in http://dev.clojure.org/jira/browse/CLJ-1569
On Wed, Mar 9, 2016 at 3:43 PM Patrick Curran <patricktheb...@gmail.com> wrote: > 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. > -- 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.
