Pack a Sequence

pack.clj

; Write a function which packs consecutive duplicates into a list
; (pack [1 1 2 1 1 1 3 3]) => '((1 1) (2) (1 1 1) (3 3)))
; (pack [[1 2] [1 2] [3 4]]) => '(([1 2] [1 2]) ([3 4])))

(defn pack [n]
  (letfn [(pack-iter [seen col curr out]
    (cond
      (empty? curr) (reverse (cons col out))
      (= seen (first curr)) (pack-iter seen (cons (first curr) col) (rest curr) out)
      :else (pack-iter (first curr) '() curr (cons col out))))]
  (pack-iter (first n) '() n '())))