gistfile1.clj

(defn concat-seq
  "Concatenate sequence of sequences into one sequence of elements
   from all sequences. Concatenation is made in a lazy fashion."
  ([e]
    (lazy-seq
        (when-let [s (seq e)]
            (let [f (first s)]
                (cons (first f) (concat-seq (rest f) (rest s)))))))
  ([r e]
    (lazy-seq
        (if-let [s (seq r)]
            (cons (first s) (concat-seq (rest s) e))
            (concat-seq e)))))