Was it once possible to expand capped print output by using ellipsis as button?

Was it once possible to expand capped print output by using ellipsis as button?

[Michael Pontus]

In case I'm not expressing myself clearly, example below should
illustrate where I'm coming from:

    (let ((print-length 2) (print-level 3))
      (pp load-history (current-buffer)))

And output from evaluating this form will look something like this:

    (("/home/michael/repos/emacs/lisp/emacs-lisp/pp.elc" pp-escape-newlines ...)
     ("/home/michael/repos/emacs/lisp/help-mode.elc"
      (require . button)
      ...)
     ...)

These ellipsis cut off the part of the node that would otherwise escape
beyond limits: print-length and print-level; as they were set above.

I have vivid memory of being able to interact with those ellipsis as
buttons, which would then expand and reveal previously invisible forms.

Please let me know that my memory does not deceive me. It's possible to
be the product of external package, but so far my searches didn't turn
up anything of this nature.

If this was in fact a feature, that was pulled out of stock emacs 
I would find it very interesting to learn about the reason that forced
such decision. 

Re: Was it once possible to expand capped print output by using ellipsis as button?

[Stefan Monnier]

> I have vivid memory of being able to interact with those ellipsis as
> buttons, which would then expand and reveal previously invisible forms.

I think your memory is right.  The NEWS file for Emacs-21 says:

   *** The commands to evaluate Lisp expressions, such as C-M-x in Lisp
   modes, C-j in Lisp Interaction mode, and M-:, now bind the variables
   print-level, print-length, and debug-on-error based on the new
   customizable variables eval-expression-print-level,
   eval-expression-print-length, and eval-expression-debug-on-error.
   
   The default values for the first two of these variables are 12 and 4
   respectively, which means that `eval-expression' now prints at most
   the first 12 members of a list and at most 4 nesting levels deep (if
   the list is longer or deeper than that, an ellipsis `...'  is
   printed).
   
   <RET> or <mouse-2> on the printed text toggles between an abbreviated
   printed representation and an unabbreviated one.

> If this was in fact a feature, that was pulled out of stock emacs 
> I would find it very interesting to learn about the reason that forced
> such decision. 

I don't think it's been removed.  I've never used it, tho, so maybe it
doesn't work any more.  If so, try M-x report-emacs-bug.


        Stefan