Tuareg, the mode for OCaml code in Emacs, has been updated last year to change how comments are working and apply a different style. I am not a big fan of the new style and will try to explain how to change it.
As an example, I am using this snippet of code, select it all and use
M-; to comment it.
let f () = let a = 1 in let b = 2 in a, b
The old comment style was like this, with each line commented individually:
(* let f () = *) (* let a = 1 in *) (* let b = 2 in *) (* a, b *)
It has been changed to this style, with only one comment for the whole block and a prefix on each line:
(* let f () = * let a = 1 in * let b = 2 in * a, b *)
The new behaviors comes from this line in tuareg:
(setq-local comment-style 'multi-line)
comment-style default value is
'indent. Which corresponds to the
old comment style described previously. Other styles are available but
won't be described here. Look for them in
C-h v RET comment-style
I don't mind to have one comment for a whole block. It makes it easier
for other editors to handle. It is less noise. But I don't like that
all lines are prefixed with a
*. Because other editors have to be
configured to remove those extra characters automatically. Because
they have to be removed by hand if a few lines are moved away from the
comment. And they are not good for accessibility.
So how to keep using only one comment but without prefix? The answer
is in the
comment-continue variable. The documentation is accessible
C-h v RET comment-continue RET.
Continuation string to insert for multiline comments. This string will be added at the beginning of each line except the very first one when commenting a region with a commenting style that allows comments to span several lines. It should generally have the same length as ‘comment-start’ in order to preserve indentation. If it is nil a value will be automatically derived from ‘comment-start’ by replacing its first character with a space.
To remove the prefix the content of
comment-continue should be
" * " to
To do so, the Emacs configuration has to be updated. I think it's better to update this behavior only while editing a file in tuareg mode and so I put the configuration in a tuareg hook.
(add-hook 'tuareg-mode-hook (lambda () (setq-local comment-continue " ")))
Now if I comment my snippet I get the expected result:
(* let f () = let a = 1 in let b = 2 in a, b *)
If you just want to go back to the old behavior, the configuration is:
(add-hook 'tuareg-mode-hook (lambda () (setq-local comment-style 'indent)))