emacs programming

So I have this reading list which has around 750 org entries. My org publish setup adds CUSTOM_ID for each entry before publishing and does a regex based removal of the extra <pre>...</pre> text generated due to the CUSTOM_ID property. The aim here is to have the items get reasonable1 section id which can then be hyperlinked to jump around but not show up the CUSTOM_ID text in the final html.

Usually the solution would be to just have programmatically generated CUSTOM_ID properties and then not export org properties drawer in html (a lot of org-publish based blogs do this). Since I wanted the drawer to show, I did this post processing thing where I would go over the generated html and remove elements like the following:

<!-- remove this whole element -->
<pre class="example">
CUSTOM_ID: sec-mathematics/logic
</pre>

<pre class="example">
AUTHOR: Timothy Gowers, June Barrow-Green, Imre Leader
ADDED: <2018-01-08>
GOODREADS: https://ww...
CUSTOM_ID: sec-the-... <!-- remove this line -->
</pre>

Anyway, here is how much my old function took:

(with-current-buffer "books.org"
  (benchmark-run (pile-publish-current-file t)))
12.937646686 2 0.3899886170000002

Since I was basically double looping over the buffer in that version, here is the results from a better version:

(with-current-buffer "books.org"
  (benchmark-run (pile-publish-current-file t)))
8.998249791 1 0.1909841450000016

I don't know why I was not worried but this is really really slow. A 500K file should not behave like this in a lightweight text processing task. Having bad timing estimates, I tried porting the same regex in Common Lisp and got almost instantaneous results.


The issue was in my mental model which conflicts with the buffer model of string manipulation in Emacs. Doing (with-current-buffer ... hides the buffer and makes me feel like I am working on plain strings, which is wrong. Since the exported file had a full fledged html buffer with all the modes and fontification enabled, it took a long time for the re-search-forward calls to go through the whole thing. Just switching the buffer mode to fundamental-mode does the trick.

Here is the current version. Even though the complete export is around 2-3 seconds, the time spent in that regex step is almost nothing.

(with-current-buffer "books.org"
  (benchmark-run (pile-publish-current-file t)))
3.134736484 2 0.49967851099999905

Footnotes:

1
By default org puts random ids like org4d43428 which also change after exports