Re: length of query-replace-history list

[Kevin Rodgers <ihs_4664@yahoo.com>]

B. T. Raven wrote:
> Thanks, Kevin. Now that I understand what's going on, it doesn't seem like
> it's worth while just to save a few hundred bytes. I had an idea to save
> the qrh into a saved association list, something like:
> 
> (setq sal (cons (cons  (cadr query-replace-history) (car
> query-replace-history)) sal))

You could use desktop-save-mode and add query-replace-history to
desktop-globals-to-save.

> The idea is to re-load this later and run query replace in batch mode on
> other files. I have no idea how to do this in detail but it seems possible
> and it would be very useful to me. Maybe instead of setting it to 2, I'll
> set it to t, and then then figure out how to manipulate the resulting flat
> list of strings after an hours' long session of query-replacing.

You could also set desktop-base-file-name to specify a file just for
this specific purpose, and save just the last elements of
query-replace-history.

,----[ C-h v desktop-save-hook RET ]
| desktop-save-hook is a variable defined in `desktop.el'.
| Its value is nil
|
| Documentation:
| Normal hook run before the desktop is saved in a desktop file.
| This is useful for truncating history lists, for example.
|
| You can customize this variable.
|
| [back]
`----

(setq desktop-base-file-name ".emacs.batch.desktop"
       desktop-globals-to-save 'query-replace-history)

(add-hook desktop-save-hook
	  (lambda ()
	    (when (cdr (cdr query-replace-history))
	      (setcdr (cdr query-replace-history) nil))))

> Since for my needs this list (sal) of dotted pairs would be a few thousand
> elements long, it is probably not the best data structure to use. Could
> something along this line be done with a hash table?

Do you want all of the history or not?  If you only want 2 elements as
you originally said, then don't bother saving and manipulating anything
else.  If you do want the whole history, a list of strings may be as
good as anything -- after all, how do you know which search and replace
strings to use?

Finally, note that you can set query-replace-from-history-variable
and query-replace-to-history-variable to different symbols, and save
them instead.

-- 
Kevin