Clojure TicTacToe show board

(defn show-board [board]
    "Prints the board on the screen.
     Board must be a list of three lists of three elements with
     :cross for a cross and :circle for a circle, other value for nothing"
    (let [
          convert-elem {:cross \X, :circle \O}
          convert-line (fn [elems-line]
                            (reduce str (map #(convert-elem % \_) elems-line)))
          ]
         (doseq [line board]
            (println (convert-line line)))))

(show-board [[:cross :circle :a] [:none :circle :none] [:cross :none :none]])