"stream fusion" example using transducers

fuse.clj

;; lots of garbage
;;
(->> coll                        ;; original collection
     (map #(assoc % :foo :bar))  ;; intermediate Chunked collection 1
     (filter :baz)               ;; intermediate Chunked collection 2
     (map :feature)              ;; intermediate Chunked collection 3
     (into []))                  ;; reduction using #'conj over Chunked collection #3

;; -- direct reduction using transducers --
;; reduction over original collection using #'conj
;; but #'conj that has been transformed by a transducer

;; the transducer is an ordinary composed function
;; the middle argument of (into [] xf coll)
;; as opposed to the macro ->> above
;; same basic internals, but the parentheses in a different spot

;; 0 intermediate collections
;; 1 reduction
(into []                        
      (comp (map #(assoc % :foo :bar)) ;; 
            (filter :baz)
            (map :feature))
      coll)