Print writer extensions for functions.

extend.clj

(defn install-fn-printers!
  "NOTE: If you are using Emacs + cider-nrepl, these two `print-method`
  implementations will not be installed. I'm currently working on a fix to get
  this enabled in the Emacs environment... But if you want to test this feature
  out, simply execute these forms.
  https://github.com/clojure-emacs/cider-nrepl/blob/master/src/cider/nrepl/print_method.clj#L42-L71

  TODO write a with-methods instead to do this..."
  []
  #?(:clj
     (do
       (defmethod print-method AFunction [f ^java.io.Writer w]
         (.write w (.toString ^Object (v/freeze f))))

       (defmethod print-method MultiFn [f ^java.io.Writer w]
         (.write w (.toString ^Object (v/freeze f)))))

     :cljs
     (extend-protocol IPrintWithWriter
       MetaFn
       (-pr-writer [x writer _]
         (write-all writer (.toString (v/freeze x))))

       MultiFn
       (-pr-writer [x writer _]
         (write-all writer (.toString (v/freeze x)))))))