Generic functions

generic-functions.lisp

;;; A generic function specifies only the interface.
;;; It performs a high-level operation.

;;; Generic functions are functions that behave differently
;;; depending on the type and identity of the arguments. 
(defgeneric say-type-of-object (x)
  (:documentation "It displays the type of an object."))

;;; The implementation of a generic function does not exist in one place; it
;;; is distributed across a set of methods.

(defmethod say-type-of-object ((x number))
  (format t "~% ~a  is a number." x))

(defmethod say-type-of-object ((x string))
  (format t "~% ~a  is a string." x))

(defmethod say-type-of-object ((x list))
  (format t "~% ~a is a list." x))

(defmethod say-type-of-object ((x symbol))
  (format t "~% ~a is a symbol." x))

(defclass person ()
  ((name :accessor name
	 :initarg :name)))

(defparameter *me* (make-instance 'person :name "Juan"))

(defmethod say-type-of-object ((x person))
  (format t "~% ~a is a person." x))