map(clojure.core)

Returns a lazy sequence consisting of the result of applying f to the set of first items of each coll, followed by applying f to the set of second items in each coll, until any one of the colls is exhausted. Any remaining items in other colls are ignored. Function f should accept number-of-colls arguments.

; clojure/core.clj:1494
(defn map
  ([f coll]
   (lazy-seq
    (when-let [s (seq coll)]
      (cons (f (first s)) (map f (rest s))))))
  ([f c1 c2]
   (lazy-seq
    (let [s1 (seq c1) s2 (seq c2)]
      (when (and s1 s2)
        (cons (f (first s1) (first s2))
              (map f (rest s1) (rest s2)))))))
  ([f c1 c2 c3]
   (lazy-seq
    (let [s1 (seq c1) s2 (seq c2) s3 (seq c3)]
      (when (and  s1 s2 s3)
        (cons (f (first s1) (first s2) (first s3))
              (map f (rest s1) (rest s2) (rest s3)))))))
  ([f c1 c2 c3 & colls]
   (let [step (fn step [cs]
                 (lazy-seq
                  (let [ss (map seq cs)]
                    (when (every? identity ss)
                      (cons (map first ss) (step (map rest ss)))))))]
     (map #(apply f %) (step (conj colls c3 c2 c1))))))

Copyright (c) Rich Hickey. All rights reserved.

The use and distribution terms for this software are covered by the Eclipse Public License 1.0, which can be found in the file epl-v10.html at the root of this distribution. By using this software in any fashion, you are agreeing to be bound by the terms of this license. You must not remove this notice, or any other, from this software.