defprotocol/defrecord example

gistfile1.clj

(defprotocol Inspect (inspect [c]))

(defprotocol Maths
  (plus     [this another])
  (multiply [this another]))

(defrecord Rational [nom den]

  Inspect
  (inspect [this] (str  (:nom this) "/"  (:den this) ))

  Maths
  (plus     [this another]
    (Rational.
      (+
        (*
          (:nom this)
          (:den another))
        (*
          (:nom another)
          (:den this)))

      (*
        (:den this)
        (:den another ))))


  (multiply  [this another]
    (Rational.
      (*
        (:nom this)
        (:nom another))
      (*
        (:den this)
        (:den another)))))