gistfile1.clj

(defn filter-collecting [predicate collector & lists]
  (lazy-seq
   (loop [lists lists out []]
     (if (empty? (first lists))
       (reverse out)
       (let [heads (map first lists)]
         (if (apply predicate heads)
           (recur (map rest lists) (cons (apply collector heads) out))
           (recur (map rest lists) out)))))))

;; usage:
;; (filter-collecting 
;;   (fn [x y] (< x y)) 
;;   (fn [x y] (+ x y)) 
;;   '(1 7 3 9) 
;;   '(5 5 5 5))
;;  ==> (6 8)