I am trying to understand transducers and am reading through https://clojure.org/reference/transducers I think I am missing something, please can someone help?
I read the part about the 'shape' of a transducer-creating-function ( https://clojure.org/reference/transducers#_creating_transducers) and made this function (defn no-op [rf] (fn ([] (rf)) ([x] (rf x)) ([x r] (rf x r)))) which I call with (pprint (eduction no-op (range 5))) and get (0 1 2 3 4) This is OK. If I now define (defn nearly-no-op [rf] (fn ([] (rf)) ([x] (let [tmp (rf x)] (* x 2))) ([x r] (rf x r)))) (I want the 'finishing' function to double the answer) Then (pprint (eduction nearly-no-op (range 5))) gives me a null pointer exception in multiply. Where does this come from? If I try (defn nearly-no-op [rf] (fn ([] (rf)) ([x] (count (rf x))) ([x r] (rf x r)))) then I get (0 1 2 3 4) again, i.e. the count doesn't play any part in the final result. Thanks in advance! Complete program: (ns ttry.core (:require [clojure.pprint :refer [pprint]]) (:gen-class)) (defn no-op [rf] (fn ([] (rf)) ([x] (rf x)) ([x r] (rf x r)))) (defn nearly-no-op [rf] (fn ([] (rf)) ([x] (let [tmp (rf x)] (* x 2))) ([x r] (rf x r)))) (defn -main [& args] (pprint (eduction (map identity) (range 5))) (pprint (eduction no-op (range 5))) (pprint (eduction nearly-no-op (range 5)))) -- 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.
