Changing map behaviour in Clojure

Question

I need to modify map function behavior to provide mapping not with minimum collection size but with maximum and use zero for missing elements.

Standard behavior:

Answer 1

Along the lines of @LeNsTR's solution, but simpler and faster:

(defn map-ext [f & colls]
  (lazy-seq
   (let [colls (filter seq colls)
         firsts (map first colls)
         rests (map rest colls)]
    (when (seq colls)
      (cons (apply f firsts) (apply map-ext f rests))))))

(map-ext + [1 2 3] [4] [5 6] [7 8 9 10])
;(17 16 12 10)

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I've just noticed Michał Marczyk's accepted solution, which is superior: it deals properly with asymmetric mapping functions such as -.