Evaluating Medley compatibility with Practical Common Lisp code: Chapter 16

[pamoroso]

Chapter 16. Object Reorientation: Generic Functions

This is a continuation of the work on issue #609. To evaluate the compatibility of Medley Common Lisp with ANSI Common Lisp I'm testing on Medley the code of the book Practical Common Lisp by Peter Seibel.

Session transcript

To test the code of chapter 16 I evaluated the expressions at a XCL Exec. I added only a few of the missing definitions and calls as some are in the next chapter and I'll get to them anyway.

All the code seems to work as expected:

2/8> (defgeneric draw (shape)
  (:documentation "Draw the given shape on the screen."))
DRAW
2/9> 

2/9> (defclass bank-account ()
  ((customer-name
    :initarg :customer-name)
   (balance
    :accessor balance
    :initarg :balance
    :initform 0)))
BANK-ACCOUNT
2/10> 

2/10> (defparameter *account*
  (make-instance 'bank-account :customer-name "John Doe" :balance 1000))
*ACCOUNT*
2/11> 

2/11> (defgeneric withdraw (account amount)
  (:documentation "Withdraw the specified amount from the account.
Signal an error if the current balance is less than amount."))
WITHDRAW
2/12> 

2/12> (defmethod withdraw ((account bank-account) amount)
  (when (< (balance account) amount)
    (error "Account overdrawn."))
  (decf (balance account) amount))
(WITHDRAW (BANK-ACCOUNT))
2/13> 

2/13> (withdraw *account* 100)
900
2/14> 

2/14> (withdraw *account* 1100)
Account overdrawn.

2/15> 

2/15> (defgeneric priority (job)
  (:documentation "Return the priority at which the job should be run.")
  (:method-combination +))
PRIORITY
2/16> 

2/16> (defgeneric priority (job)
  (:documentation "Return the priority at which the job should be run.")
  (:method-combination + :most-specific-last))

New GENERIC-FUNCTIONS definition for PRIORITY.
PRIORITY
2/17> 

2/17> (defgeneric beat (drum stick)
  (:documentation
   "Produce a sound by hitting the given drum with the given stick."))
BEAT
2/18>