ASM MOP example featuring inheritance and multimethod dispatch.

gistfile1.lisp

(defclass Point (Object)
  'x 'y)

#; A constructor
(defmethod initialize ((p Point) initargs)
  (call-next-method)
  (initialize-slots p initargs))

#; Point3D inherits the ctor
(defclass Point3D (Point)
  'z)

(defvar p1 (new Point 'x 1 'y 2))
(defvar p2 (new Point 'x 2 'y 3))
(defvar p3 (new Point3D 'x 5 'y 5 'z 5))

#; Generic, multiple-dispatch method
(defgeneric distance)
(defmethod distance ((a Point) (b Point))
  (write "Point * Point\n")
  (distance (new Point3D 'x (a 'x) 'y (a 'y) 'z 0)
            (new Point3D 'x (b 'x) 'y (b 'y) 'z 0)))

(defmethod distance ((a Point) (b Point3D))
  (write "Point * Point3D\n")
  (distance b a))

(defmethod distance ((a Point3D) (b Point))
  (write "Point3D * Point\n")
  (distance a (new Point3D 'x (b 'x) 'y (b 'y) 'z 0)))

(defmethod distance ((a Point3D) (b Point3D))
  (write "Point3D * Point3D\n")
  (defvar dx (- (b 'x) (a 'x)))
  (defvar dy (- (b 'y) (a 'y)))
  (defvar dz (- (b 'z) (a 'z)))
  (pow (reduce + (tuple (* dx dx) (* dy dy) (* dz dz)) 0) 0.5))

(distance p1 p2)
(distance p3 p1)
(distance p2 p3)
(distance p3 p3)

#; Prints:
#; Point * Point
#; Point3D * Point3D
#; Point3D * Point
#; Point3D * Point3D
#; Point * Point3D
#; Point3D * Point
#; Point3D * Point3D
#; Point3D * Point3D