Subject: bug#25122: 24.5; function describe-variable hangs on large variables

From: [email-masked]
Date: Sat, 11 Mar 2017 10:35:24 -0500

Stefan Monnier <[email-masked]> writes:

>>           (cl-letf (((symbol-function 'pp)
>>                      (lambda (object &optional stream)
>>                        (let ((fn (lambda (ob &optional stream)
>>                                    (princ (pp-to-string ob)
>>                                           (or stream standard-output))
>>                                    (terpri)))
>>                              (print-circle t))
>>                          (if (consp object)
>>                              (progn
>>                                (insert "\n(")
>>                                (mapc fn object)
>>                                (cl-letf (((point) (1- (point))))
>>                                  (insert ")")))
>>                              (funcall fn object stream))))))
>
> Hmm... I wonder why this would be faster.  In the past, the
> implementation of `print-circle` had a poor complexity, but we fixed
> that around Emacs-24, IIRC so it now uses a hash-table and should have
> O(n) complexity, which means that pp shouldn't be slower than (mapc
> #'pp).

I think it's because when we indent-sexp only on individual entries, we
don't parse as far back.