f should be a function of 2 arguments. If val is not supplied, returns the result of applying f to the first 2 items in coll, then applying f to that result and the 3rd item, etc. If coll contains no items, f must accept no arguments as well, and reduce returns the result of calling f with no arguments. If coll has only 1 item, it is returned and f is not called. If val is supplied, returns the result of applying f to val and the first item in coll, then applying f to that result and the 2nd item, etc. If coll contains no items, returns val and f is not called.
; clojure/core.clj:516 (defn reduce ([f coll] (let [s (seq coll)] (if s (if (instance? clojure.lang.IReduce s) (. #^clojure.lang.IReduce s (reduce f)) (reduce f (first s) (next s))) (f)))) ([f val coll] (let [s (seq coll)] (if (instance? clojure.lang.IReduce s) (. #^clojure.lang.IReduce s (reduce f val)) ((fn [f val s] (if s (recur f (f val (first s)) (next s)) val)) f val s)))))
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