Editing files with one-sentence-per-line

Question

A bit of background.

I’m trying to version-control my latex documents, and the effectiveness of this initiative would be greatly improved if I adopt a one-sentence-per-line approach.

For instance, the following is what my documents will look like.

Some text here.
New stencence on the same paragraph.
Some more text, still on the same paragraph.

This is another paragraph.

My question is simple.
How much of that can I automate/improve with Emacs?

The following two points are what I have in mind.

1. My sentences are long, so I need to wrap lines without actually filling them. That is, a very long sentence needs to be displayed over several lines on my screen, but it needs to be a single line in the “.tex” file. This would preferably be done in a way that doesn’t wrap equations.

   visual-line-mode wraps at window width, that is too wide. I need something that wraps lines and limits their width to 80 or so characters. Just like fill-paragraph would normally do, but without actually breaking the lines in the file.

2. I can manually break the line after each sentence, but it would be highly preferable if I could configure fill-paragraph (or maybe even auto-fill-mode) to put one sentence per line as well.

Answer 1

If you just want something like visual-line-mode but configurable, you can try longlines-mode which is what I use for most of my prose. longlines-mode wraps your text similarly to visual-line-mode with the width configured by fill-column.

Here's a screenshot with fill-column set to 70 (the window actually extends even more to the right).

Configuring fill-paragraph would be neat, but I'm not sure how to do it. Instead, here's a reasonable temporary hack: make your . character electric in TeX mode, inserting a newline. This just involves rebinding it in whatever the appropriate mode hook is:

(defun my-electric-dot ()
  (interactive)
  (insert ".\n"))
(defun my-tex-hook ()
  (local-set-key (kbd ".") 'my-electric-dot))
(add-hook 'TeX-mode-hook 'my-tex-hook)

Answer 2

For (1), I would use an enlarged margin, so that visual-line-mode wraps lines at the desired fill-column. This will affect both text lines and equations, though.

As for (2), one can define a custom filling command to be bound to M-q and correctly fill paragraphs. I haven't yet managed to write a command with the correct behaviour for auto-filling.

Wrapping this all in a minor mode could look like the following. It is not very beautiful code, but should work in most cases. (I have had the unfill-paragraph function in my init.el for quite some time without noticing problems).

(define-minor-mode ospl-mode
  "One Sentence Per Line"
  :init-value nil
  :lighter " ospl"
  :keymap (let ((map (make-sparse-keymap)))
            (define-key map (kbd "M-q") 'ospl/fill-paragraph)
            map)

  (if ospl-mode
      (progn
        (visual-line-mode 1)
        (setq right-margin-width (- (window-body-width) fill-column)))
    (visual-line-mode -1)
    (setq right-margin-width 0))

  ;; Account for new margin width
  (set-window-buffer (selected-window) (current-buffer)))


(defun ospl/unfill-paragraph ()
  "Unfill the paragraph at point.

This repeatedly calls `join-line' until the whole paragraph does
not contain hard line breaks any more."
  (interactive)
  (forward-paragraph 1)
  (forward-paragraph -1)
  (while (looking-at paragraph-start)
    (forward-line 1))
  (let ((beg (point)))
    (forward-paragraph 1)
    (backward-char 1)
    (while (> (point) beg)
      (join-line)
      (beginning-of-line))))


(defun ospl/fill-paragraph ()
  "Fill the current paragraph until there is one sentence per line.

This unfills the paragraph, and places hard line breaks after each sentence."
  (interactive)
  (save-excursion
    (fill-paragraph)         ; takes care of putting 2 spaces if needed
    (ospl/unfill-paragraph)  ; remove hard line breaks

    ;; insert line breaks again
    (let ((end-of-paragraph (make-marker)))
      (save-excursion
        (forward-paragraph)
        (backward-sentence)
        (forward-sentence)
        (set-marker end-of-paragraph (point)))
      (forward-sentence) 
      (while (< (point) end-of-paragraph)
        (just-one-space)
        (delete-backward-char 1)
        (newline)
        (forward-sentence))
      (set-marker end-of-paragraph nil)))) 

Answer 3

Would your version-control issues be avoided/resolved if you use git diff --color-words or latexdiff? Then you can look at changed words.

Answer 4

One way of improving this that I have used (at times) for several years is to display sentences with line breaks as flowing after each other by folding the line breaks using the facilities of tex-fold (a part of AUCTeX).

This means that this

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Mauris pellentesque fringilla justo, quis dapibus velit tincidunt quis?
Quisque varius ligula arcu, ut imperdiet risus maximus nec.

is folded to

Lorem ipsum dolor sit amet, consectetur adipiscing elit⁎ Mauris pellentesque fringilla justo, quis dapibus velit tincidunt quis❓  Quisque varius ligula arcu, ut imperdiet risus maximus nec⁎

I've recently put this together as a minor mode in a package. Perhaps someone else will also find this useful: https://github.com/andersjohansson/tex-fold-linebreaks

Answer 5

Jan Seeger has made Twauctex. One of the features it provides is

Enable one-sentence-per-line mode.

It says:

Usage

Simply write your latex as you would normally. twauctex will take care of breaking the line whenever you enter a space after a sentence end. If the standard settings do not agree with you, use (customize-group 'twauctex), and you can customize the builtin configuration.

At the time of writing this, the package is not available on MELPA. You need to following installation instructions as provided on the GitHub repo page of Twauctex.