Pascal's triangle, iterative

gistfile1.clj

(defn pascals-triangle []
  "Return a lazy seq of rows of Pascal's triangle."
  (letfn [(next-row [row]
            (reduce (fn [v' v] (conj v' (apply +' (take 2 v)))) ; (take 2) returns [1] at the right edge
                    [1]                                         ; Left edge
                    (take (count row) (iterate rest row))))]
    (iterate next-row [1])))