gistfile1.clj

(defn product
  ([] [])
  ([xs] (if (empty? xs) [] (seq xs)))
  ([xs & rest]
    (for [x xs p (apply product rest)] (flatten (list x p)))))

(defn endless-product [xs]
  (let [repeat-xs (map #(repeat % xs) (drop 1 (range)))]
    (apply concat (map #(apply product %) repeat-xs))))

(comment
  (take 13 (endless-product "abc"))
  '(\a \b \c (\a \a) (\a \b) (\a \c) (\b \a) (\b \b) (\b \c) (\c \a) (\c \b) (\c \c) (\a \a \a))
  (take 2 (drop 10000 (endless-product "abc")))
  '((\a \a \a \a \b \c \c \c \b) (\a \a \a \a \b \c \c \c \c))
)