# Customizing tab behavior for "%" comment in prolog-mode (emacs)
**URL:** https://swi-prolog.discourse.group/t/customizing-tab-behavior-for-comment-in-prolog-mode-emacs/1927
**Category:** Tools
**Created:** [February 27, 2020, 4:39pm UTC](https://swi-prolog.discourse.group/t/customizing-tab-behavior-for-comment-in-prolog-mode-emacs/1927 "2020-02-27T16:39:36Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@peter.ludemann](https://swi-prolog.discourse.group/u/peter.ludemann)
#### Post date: [February 27, 2020, 4:39pm UTC](https://swi-prolog.discourse.group/t/customizing-tab-behavior-for-comment-in-prolog-mode-emacs/1927/1 "2020-02-27T16:39:36Z")
I’m using [Stefan Bruda’s Prolog mode for emacs](https://bruda.ca/emacs/prolog_mode_for_emacs) but I find the behavior with tab and “%” to be annoying … it always indents comments to column 32 (variable `comment-column`), even for lines starting with “%!”.
How can I change this behaviour? If I set `comment-column` to 0, then single-line comments get indented incorrectly:
```prolog
foo :-
% this is a comment
bar.
```
instead of
```prolog
foo :-
% this is a comment
bar.
```
and if I leave `comment-column` at 32, then I get the following, which I don’t want:
```prolog
%! foo is det.
foo :-
% this is a comment
bar.
```
---
### Author:  [@jamesnvc](https://swi-prolog.discourse.group/u/jamesnvc)
#### Post date: [February 28, 2020, 1:24am UTC](https://swi-prolog.discourse.group/t/customizing-tab-behavior-for-comment-in-prolog-mode-emacs/1927/3 "2020-02-28T01:24:52Z")
I think I’ve linked this to you before, but I’m using a [slightly-modified version of the prolog.el](https://github.com/jamesnvc/dotfiles/blob/9e13ea5a176fbc2989640362b6bbb0c1d7511dcb/emacs.d/modules/prolog.el) that I think comes with Emacs that doesn’t seem to have this issue with indenting (I originally started working on this to fix the indentation of terms with dictionaries & character things like `0'.`).
> [@EricGT](#):
>
> we should have a new category for the tools
Probably a good idea…
---
### Author:  [@chansey97](https://swi-prolog.discourse.group/u/chansey97)
#### Post date: [December 11, 2021, 9:31am UTC](https://swi-prolog.discourse.group/t/customizing-tab-behavior-for-comment-in-prolog-mode-emacs/1927/4 "2021-12-11T09:31:29Z")
I met the same problem recently, but it seems to have been fixed by:
```prolog
(setq prolog-align-small-comments-flag nil)
```
Then the single-line comments get indented:
```prolog
foo :-
% this is a comment
bar.
```
> One new customizable variable has been added in version 1.28:
>
> **prolog-align-small-comments-flag** (group “Prolog Indentation”) specifies how to handle “small” comments (the ones that start with a simgle “%”) as follows: When this variable is non-nil (default) small comments are aligned to `comment-column' (default 32) in all circumstances. When the variable is set to nil however small comments that begin a line (blank characters notwithstanding) will be treated just like “large” comments (the ones that start with “%%”). Note that small comments that start somewhere other than at the beginning of the line are still aligned to `comment-column’.
---
### Author:  [@chansey97](https://swi-prolog.discourse.group/u/chansey97)
#### Post date: [December 11, 2021, 10:17am UTC](https://swi-prolog.discourse.group/t/customizing-tab-behavior-for-comment-in-prolog-mode-emacs/1927/5 "2021-12-11T10:17:52Z")
Also, [the latest version (1.29)](https://bruda.ca/_media/emacs/prolog.el) has a bug, I don’t know if it exists in the old version though, is that `prolog-indent-buffer` doesn’t work properly in some cases. The root cause is that the `prolog-indent-line` may throw an error “Beginning of buffer”.
It could be work around by advising:
```prolog
(defun prolog-indent-line/around (orig-fun &rest args)
(save-excursion
(condition-case nil
(apply orig-fun args)
(beginning-of-buffer 'noindent))))
(advice-add 'prolog-indent-line :around #'prolog-indent-line/around)
```
PS. At the writing time, [Stefan Bruda’s Prolog mode for emacs](https://bruda.ca/emacs/prolog_mode_for_emacs)’ website said the prolog-mode is version 1.28, but it is actually 1.29. This may cause some confusion.