bug#15233: pp-eval-expression: Signature parity with `eval-expression'

[Jambunathan K <kjambunathan@gmail.com>]

Drew Adams <drew.adams@oracle.com> writes:

>> eval-expression takes INSERT-VALUE.  But `pp-eval-expression' doesn't.
>> But it should.
>
> FWIW -
>
> Done 5 years ago in pp+.el (and probably suggested to Emacs Dev as well).
> http://www.emacswiki.org/emacs-en/download/pp%2b.el

I haven't used pp+.el before.  So consider two independent
upvotes... for this request.

To add to your list:

1. Undo in pp eval outputs.  (There is a separate bug for that)

2. Linkify circular references.  So that when I click on a circular
   "reference" it takes me to the "site of definition".

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The above two requests are not hypothetical requests.  

The new `org-element.el' library lispifies an Org buffer and it uses
`:parent' pointers to boot.  So, for complex outlines and for operations
that non-trivially manipulate the lisp tree, examining, manipulating and
persisting a lisp tree is a REAL need.