Replace print by Tims

gistfile1.clj

(defonce old-print-method-impl print-method) ; the clojure.lang.MultiFn instance itself

(def ^:dynamic *overriding-print-method* false)

(defn print-method-override-dispatch [x writer]
  (if *overriding-print-method*
    (type x)
    :default))

(defmulti print-method-override #'print-method-override-dispatch)

(defmethod print-method-override :default [x writer]
  (old-print-method-impl x writer))

(defmethod print-method-override clojure.lang.Keyword [x writer]
  (if (= x :snake)
    (.Write writer "I bet you wanted to print \":snake\"")
    (old-print-method-impl x writer)))

(alter-var-root #'print-method (constantly #'print-method-override))

;; ------------------------------------------------------------

(println [:dog :snake :cat])
;; => [:dog :snake :cat]

(binding [*overriding-print-method* true]
  (println [:dog :snake :cat]))
;; => [:dog I bet you wanted to print ":snake" :cat]