Transducers 101

Introduction to Transducers

Links
http://clojure.com/blog/2012/05/08/reducers-a-library-and-model-for-collection-processing.html
http://blog.cognitect.com/blog/2014/8/6/transducers-are-coming
http://clojure.org/transducers
http://clj-me.cgrand.net/2014/09/11/the-rules-of-transducer-club/
http://clj-me.cgrand.net/2014/10/08/these-arent-the-reducing-functions-you-are-looking-for/
https://vimeo.com/45561411
https://www.youtube.com/watch?v=6mTbuzafcII
http://go.cognitect.com/core_async_webinar_recording

Záznam - https://www.youtube.com/watch?v=-hwWZkqQO9w#t=2169

Transcript

1. Transducers 101 @alesroubicek
3. Data-flow combinators ;; nested calls (reduce + (filter odd? (map #(+ 2 %) (range 0 10)))) ;; functional composition (def xform (comp (partial filter odd?) (partial map #(+ 2 %)))) (reduce + (xform (range 0 10))) ;; threading macro (defn xform [xs] (->> xs (map #(+ 2 %)) (filter odd?))) (reduce + (xform (range 0 10)))
4. Reducers ;; clojure.core.reducers (def xform (comp (r/filter odd?) (r/map #(+ 2 %)))) (reduce + (xform (range 0 10)))
5. Transducers ;; transducers (def xform (comp (map #(+ 2 %)) (filter odd?))) (transduce xform + (range 0 10)) (sequence xform (range 0 10)) (into [] xform (range 0 10)) (chan 1 xform) (r/fold + (xform +) (range 0 10))
6. How it works? Unary function that returns transformer • Initialization (Nullary step function variation) (f) • Step function (Binary function variation) (f result input) • Early termination (reduced result) • Completion (Unary step function variation) (f result) Polymorphic CollReduce Can have state (volatile)
7. FAQ Are they lazy? Are they eager? Do they run in parallel? Are they faster? How they save my time? Are you drunk?
8. Transducers summary Pure recipes (what to do) w/o knowledge how to do it Composable Reusable (seqs, channels, [parallel, observables…]) Efficient (no intermediate results) Natural flow Never call transducers directly!
9. Where to go next? http://clojure.com/blog/2012/05/08/reducers-a-library-and-model-for-collection- processing.html http://blog.cognitect.com/blog/2014/8/6/transducers-are-coming http://clojure.org/transducers http://clj-me.cgrand.net/2014/09/11/the-rules-of-transducer-club/ http://clj-me.cgrand.net/2014/10/08/these-arent-the-reducing-functions-you-are- looking-for/ https://vimeo.com/45561411 https://www.youtube.com/watch?v=6mTbuzafcII http://go.cognitect.com/core_async_webinar_recording