Bruce Tobin wrote:
> 
>  I have a very basic understanding of the condition system, e.g. how to
> use (ignore-errors) and (handler-case).  ...
> 
>  Here's the kind of thing I want to be able to handle.  Suppose
> I design a dialog with one button, whose set-value-fn is
> 
> (defun button-1-set-value-fn (x y z)
>   (error "Oops! Wrong button!"))
> 
> Now I want to be able to run this dialog, trapping this and any other
> errors that may be generated by functions called from the dialog's event
> loop. I tried
> 
>   (ignore-errors (dialog-1))
> 
>  but this of course did not trap the error.  Obviously I don't want to
> have to put error-trapping code at the beginning of every event-handling
> function, but what is my alternative?

I presume you have an outer loop that calls process-pending-events (or
is it single-event that doesn't block?).  First, IMHO you should never
call error but always define and signal your own condition types.  You
should also, as I show below, provide a nice way to catch system
errors.  Let's see if I can produce something you can easily enough
follow.  Let me know if it's too muddled.  I'm just following our basic
flow but writing extemporaneous code; so, I won't guarantee that it
runs, but it can't be far wrong.

(define-condition my-applications-conditions ()
  (;any slots you want all your applications conditions to have such as
   (default-restart
     :reader default-restart
     :initarg :default-restart
     :documentation "if present, is either a symbol naming the restart,
a list whose                      car is the restart name and cdr is the
list of args, or a restart object.  Of course, the code below is too
lazy to handle anything but a symbol or restart object."))
   (:default-initargs :default-restart nil)
   ;;what to say to the user
   (:report (lambda (condition stream)
               (format stream "This wonderous application signalled an
abnormal <[ at condition~> and wants to jump to ~A~]."
                    (find-restart
                       (if (consp (default-restart condition))
                         (car (default-restart condition))
                         (default-restart condition))
                        condition)))))

(define-condition bad-button (my-applications-conditions)
  (;;whatever slots make sense such as
   (help-context
     :type integer
     :initarg :help-context
     :reader help-context
     :documentation "The help context to pass to WinHelp to get relevant
information for when this button applies.")
   ;;or
   (simple-explanation ;...
      ...))
   (:report (lambda (condition stream)
                 (format stream "..." ...))))

;;even a specific condition for each button
(define-condition bad-button-quux (bad-button) ...)

;;in your button action fn, you'd then signal the right type of
condition
(defun button-1-set-value-fn (x y z)
  (restart-case
   (signal 'bad-button-quux
       :simple-explanation "You may only ask for dessert after you eat
your vegetables"
       :default-restart 's-all-right)
   (s-all-right ()
     :test (lambda (condition) (typep condition 'bad-button-quux))
     :report "Oh, yeah, just ignore the button press, thanks.")
   (just-eat-the-vegies-for-me ()
     :test (lambda (condition) (typep condition 'bad-button-quux))
     :report (lambda (stream)
               (format stream "Go ahead and eat ~A with ~A for me."
                    x z))
     (eat-vegies x z))))

;;in your top loop

(restart-case
 (loop 
   do (handler-bind 
        ((my-applications-conditions #'my-applications-handler)
         (t #'my-application-system-error-handler))
        (process-pending-events)
        ;; anything else in my main loop
       ))
 (exit-and-farewell ()
   :test true
   :report "Exit this wonderous application"))
;;given the above restart, you can define the exit menu choice as 
 ... (invoke-restart 'exit-and-farewell))

;;you could even define my-applications-conditions as a method 
;;and specialize it for different types of conditions
(defun my-applications-conditions (condition)
   ;;important, wrap the body w/ a handler-bind b/c you're 
   ;;outside your top loop handler.  You don't need to wrap
   ;;any other fn bodies with handler-bind except for 
   ;;my-application-system-error-handler
   (handler-bind
        ((my-applications-conditions #'my-applications-handler)
         (t #'my-application-system-error-handler))
     (let* ((restarts (restarts-with-default-first condition))
            ;;actually, you should ensure that your top window 
            ;;is shown (not minimized). Define what happens when the
user 
            ;;hits <escape>.
            (choice (a-single-item-list-dialog (or *my-top-window*
*screen*) 
                        "August Wizarg"
                        (format nil "~A" condition)
                        (mapcar #'princ-to-string restarts))))
        (invoke-restart (nth choice restarts)))))
         
(defun restarts-with-default-first (condition)
  (let ((restarts (compute-restarts condition)))
    (if (default-restart condition)
        (cons (find (default-restart condition) restarts :key
#'restart-name)
              (delete (default-restart condition) restarts :key
#'restart-name))
         restarts)))         

;;my-application-system-error-handler would be similar to
my-applications-conditions
;;except should know that some errors are irrecoverable such as out of
stack/
;;out of memory and you can do more harm by trying to open a dialog in
those cases.
;;Of course, Franz doesn't have much of a condition hierarchy nor even
well documented
;;condition strings; so, you kind of have to do partial string matching
on the basis
;;of lessons learned or guesses.  Another aspect of this is for errors
like out of 
;;disk space, you may want to provide additional advice beyond the error
message.
-- 
Donald H. Mitchell              <pgh.net at dhm>
Proactive Solutions, Inc.       412.835.2410
5858 Horseshoe Dr.              412.835.2411 (fax)
Bethel Park, PA 15102