_Comment made by: petterik_
I've experimented with making eduction use chunked-seq optimizations and it's about twice as fast. The same code works with clojure.core/sequence and I see the same performance speed up there as well.
I don't know how we feel about external links but here's a gist with:
* Code
* Tests
* Output from running (-main)
* One-line commands to test it out with clj and cljs.main
https://gist.github.com/petterik/0e0c9bcc4b223c01bbb1442e820ea503
The code for sequence looks like this:
(defn- chunked-sequence [xform s]
(let [xf (xform conj!)
rrf #?(:clj (#'clojure.core/preserving-reduced xf)
:cljs (#'cljs.core/preserving-reduced xf))
step (fn self [v s]
(if-not s
(persistent! (xf v))
(let [c (chunk-first s)
;; Calling unreduced for :clj to get the same
;; behaviour as :cljs
#?@(:clj [chunk (unreduced (.reduce c rrf v))]
:cljs [chunk (reduce rrf v c)])]
(if (reduced? chunk)
(seq (persistent! (xf (deref chunk))))
(let [next-chunk (chunk-next s)]
(if (zero? (count chunk))
(lazy-seq
(self v next-chunk))
(lazy-cat
(persistent! chunk)
(self (transient []) next-chunk))))))))]
(step (transient []) (seq s))))
(defn sequence2 [xform coll]
(let [s (seq coll)]
(if (chunked-seq? s)
(seq (chunked-sequence xform coll))
(sequence xform coll))))
