It all started innocently enough. I had a deftype that was implementing several protocols. I had written all of the protocol functions inside the body of the deftype. And even though each function, by itself, wasn’t overly large, the entire blob of code was getting out of hand.

Here is a tiny little example with some made-up protocols and a type that embedded the protocol implementation inside the deftype. In the actual code there were many more methods that needed to be implemented.

(defprotocol Proto1
  (p11 [this])
  (p12 [this foo bar]))
(defprotocol Proto2
  (p21 [this])
  (p22 [this baz bin]))
(deftype MyType [item1 item2 item3 item4]
  Proto1
  (p11 [this] ...)
  (p12 [this foo bar] ...)
  Proto2
  (p21 [this] ...)
  (p22 [this baz bin] ...))