8.5 Examples

This example illustrates "typical" use of action lists. The define-action forms might be scattered across several files (mail-utilities.lisp, caffeine.lisp, and so on). Each of the functions, such as read-mail, dont-panic, and so on, take one argument: hassled-p.

(in-package "CL-USER")

(define-action-list "On arrival at office"
    :documentation "Things to do in the morning"
    :dummy-actions '("Look busy")
    :default-order '(:before "Look busy"))

(define-action "On arrival at office" "Read mail" 'read-mail)

(define-action "On arrival at office" "Greet co-workers" 
                 'say-hello)

(define-action "On arrival at office" "Drink much coffee" 
                 'wake-up:after "Locate coffee machine")

(define-action "On arrival at office" "Locate coffee machine"
                 'dont-panic)

(defun my-morning (hassled-p Monday-p)
   (execute-actions ("On arrival at office" 
                     :ignore-errors-p Monday-p)
                 hassled-p)
    ...rest of my-morning code goes here...)

The next example illustrates use of execution-functions and post-processing.

Here are the implementation details, which are hidden from the "user":

(in-package "CL-USER")
 
(defstruct (thing (:constructor make-thing (name number)))
  name
  number)

(defvar *things* 
  (make-unregistered-action-list :sort-time :define-action
         :execution-function 'act-on-things))

(defun do-things (function &optional post-process)
  (execute-actions (*things* :post-process post-process)
                   function))

(defun act-on-things (things other-args-list &key post-process)
  (with-action-list-mapping
   (things ignore thing post-process)
   (destructuring-bind
    (function) other-args-list
    (funcall function thing))))

The interface is given below. The internals of the mapping mechanism are hidden.

(in-package "CL-USER")
 
(defmacro define-thing (name number)
  (with-unique-names (thing)
    `(let ((,thing (make-thing ,name ,number)))
       (define-action *things* ',name ,thing))))

(defmacro undefine-thing (name)
  `(undefine-action *things* ,name))

(defun find-thing (name)
  (do-things #'(lambda (thing)
                   (and (equal name (thing-name thing))
                        thing))
               :or))

(defun add-things ()
  (reduce '+ (do-things 'thing-number :collect)))