visitor.clj

(defn visitor
  "Used to implement visitor patterns.  (first (args)) is modified by the visitor function"
  [visit-fn return-fn]
  (fn [f & args]
    (return-fn
     (apply f (visit-fn (first args)) (rest args)))))

(defn visitor*
  [visit-fn return-fn]
  (fn [f & args]
    (let [r-args (reverse args)
	  mod-args (conj (rest r-args) (visit-fn (first r-args)))]
    (return-fn
     (apply f (reverse mod-args))))))

(def visit-keyword (visitor name keyword))

(def visit-symbol (visitor name symbol))