Programming Clojure, 2nd Edition

Moving Beyond Simple Dispatch

Clojure’s print function prints various “sequencey” things as lists. If you wanted my-print to do something similar, you could add a method that dispatched on a collection interface high in the Java inheritance hierarchy, such as Collection:

(require '[clojure.string :as str])
(defmethod my-print java.util.Collection [c]
  (.write *out* "(")
  (.write *out* (str/join " " c))
  (.write *out* ")"))

Now, try various sequences to see that they get a nice print representation:

(my-println (take 6 (cycle [1 2 3])))
| (1 2 3 1 2 3)
-> nil

(my-println [1 2 3])
| (1 2 3)
-> nil

Perfectionist that you are, you cannot stand that vectors print with rounded braces, ...