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

From: Thierry Volpiatto <[email-masked]>
Date: Sat, 11 Mar 2017 20:26:56 +0100

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.

However it is fast, it is anyway better than the actual situation were e.g C-h v
load-history takes minutes in the best case to load the 1.8M help buffer.
With this code it takes around 1s.

> 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).

The code above run at the same speed with and without print-circle...

-- 
Thierry