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Re: Getting help for a widget

From: Lennart Borgman
Subject: Re: Getting help for a widget
Date: Sun, 02 Apr 2006 11:30:34 +0200
User-agent: Thunderbird 1.5 (Windows/20051201)

Richard Stallman wrote:
    This is perhaps the main difficulty of working with or even talking about
    widgets (and, so, with Customize too) as either a user or a casual
    developer: understanding what the &address@hidden is going on.

I agree.  I find it very hard to understand that code.

But what does it mean to "get help for a widget"?
It is not clear to me, and maybe there is more than one
kind we need.

    If you press

        C-h k

on a file you get help for `widget-button-press'. But what does the button do?

I don't really follow that, but it seems to be a request
for a better answer to the question, "What happens if i click here"?

That could be useful, and perhaps C-h k ought to make a special
case for the function widget-button-press.  That would not be hard.
But where can it get the useful doc string to display?

Meanwhile, this would not help people who are doing programming with
widgets.  They need a different kind of help.

In other words, it will take some real thought and study to figure out
what "good help for widgets" would mean.  It would be useful for
people to start exploring this now.

As a little starter the two functions below can be used. The first one is new. Pub point over a widget or button and do

   M-x describe-field

This will open the widget browser. Badly needed in this are back and forward buttons (widgets of course ;-). Also badly needed IMHO are links to where widget-create are called. Can anyone explain how to add this? The information is available to the debugger, but is there a fast and simple way to get this information in `widget-create'?

The second function just makes links out of descriptions that are function names.

(defun describe-field(pos &optional use-mouse-action)
 (interactive (list (point)))
 ;; widget-browse-at
 (let* ((field (get-char-property pos 'field))
    (wbutton (get-char-property pos 'button))
    (doc (get-char-property pos 'widget-doc))
    (widget (or field wbutton doc)))
   ;;(message "widget=%s" widget)(sit-for 1)
   (if (and widget
            (if (symbolp widget)
                (get widget 'widget-type)
              (and (consp widget)
                   (get (widget-type widget) 'widget-type))))
       (widget-browse-at pos)
     ;; push-button
     (let ((button (button-at pos)))
       ;;(message "button=%s" button)(sit-for 1)
       (if button
           (let ((action (or (and use-mouse-action
                                  (button-get button 'mouse-action))
                             (button-get button 'action))))
             (message "action=%s" action)(sit-for 1)
             (describe-function (intern-soft action)))
         (message "No widget or button at point"))))))

(defun widget-browse-sexp (widget key value)
 "Insert description of WIDGET's KEY VALUE.
Nothing is assumed about value."
 (let ((pp (condition-case signal
       (pp-to-string value)
         (error (prin1-to-string signal)))))
   (when (string-match "\n\\'" pp)
     (setq pp (substring pp 0 (1- (length pp)))))
   (if (cond ((string-match "\n" pp)
         ((> (length pp) (- (window-width) (current-column)))
         (t t))
         ;;(message "pp=<%s>" pp) (sit-for 1)
         (let ((pp-sym (intern-soft pp)))
         (if (and pp-sym
                  (fboundp pp-sym))
             (widget-create 'push-button
                            :tag pp
                            :value pp
                            :action '(lambda (widget &optional event)
(let ((pp-symf (intern-soft (widget-get widget :value))))
                                         (describe-function pp-symf)))
           (widget-insert pp))))
     (widget-create 'push-button
            :tag "show"
            :action (lambda (widget &optional event)
                  "*Pp Eval Output*"
                (princ (widget-get widget :value))))

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