cum-fn.clj

;; as pointed out by Alexander Stoddard:
;; re-invention of clojure.core/reductions
;;
(defn cum-fn
  ([s cfn]
     (cond (empty? s) nil
           (empty? (rest s)) (list (first s))
           :else (lazy-seq (cons (first s) (cum-fn (first s) (rest s) cfn)))))
  ([x s cfn]
     (cond (empty? s) nil
           (empty? (rest s)) (list (cfn x (first s)))
           :else (lazy-seq (cons (cfn x (first s)) (cum-fn (cfn x (first s)) (rest s) cfn))))))