(defstruct shape ()
  (pos-x 0.0) (pos-y 0.0))

(defstruct circle (shape)
  radius
  (:method print (me stream pretty-p)
    (if pretty-p
      (put-string `#<circle of radius @{me.radius} at coordinates (@{me.pos-x}, @{me.pos-y})>`)
      :)))

(let ((circ (new circle radius 5.3)))
  (prinl circ)    ;; print machine readably
  (pprinl circ))  ;; print pretty