reduce-to.clj

(defn reduce-to [n coll]
  (lazy-loop [[f & r :as s] (rest coll)
              c (first coll)]
    (if f
      (if (< c n)
        (lazy-recur r (+ c f))
        (cons c (reduce-to n s)))
      (when c [c]))))

(defn reduce-to [n coll]
  (lazy-seq
   (loop [[f & r :as s] (rest coll)
          c (first coll)]
     (if f
       (if (< c n)
         (recur r (+ c f))
         (cons c (reduce-to n s)))
       (when c [c])))))