How can I split paragraph into one-line-per-sentence but still keep it wrapped visually?

Question

This is similar to Editing files with one-sentence-per-line (in function as well as motive), but I wish to have a full, flowing paragraph rather than visual breaks at every sentence.

I would like to have a minor mode that, when active, will visually join lines from the same paragraph (not separated by \n\n or paragraph-separate or ...) and then activate behavior (perhaps derived from visual-line-mode) that will wrap the line without actually inserting \n.

Does such a mode exist? If not, how would I go about the process of altering a paragraph's display properties to achieve the result? (After all, this is the crux of such a mode and one could be developed from the snippet.)

Answer 1

As Tom said, putting a display property on the newlines will kind of work.

The problem is to figure out which lines to wrap.

Here is an example to get you started:

(let ((eol-regexp "[[:graph:]] ?\\(\n\\)[^\t\n ]"))
  (font-lock-add-keywords nil
   `((,eol-regexp 1 '(face default display " ")))))

(visual-line-mode 1)

This will "remove" newlines if it is preceded by graphical characters and the next line is not indented or empty. You will have to experiment to find something that works for you.

Some more explanations:

1. font-lock-add-keywords adds a list of rules to font locking (so font lock must be enabled. The first argument can be a mode (e.g. text-mode); in our case it is nil, which means add the rule only for the current buffer.
2. Our "rule" is (,eol-regexp 1 '(face default display " ")). The first element is the regular expression we built earlier; the second is the subexpression we are interested in; the third is the "face" we want to apply.
3. While using a face for the newlines is of no use for us, we can also add text properties. So we use the default face and than add a display property witch replaces the substring 1 (i.e. the newline) with a space.
4. If you shoot yourself in the foot, delete the buffer or remove the keyword with font-lock-remove-keywords.
5. You might also want to add display to font-lock-extra-managed-props (I have not tried this).
6. The tricky part is to get the regexp right. "\(\n\)[^\n]" would match any newline that is not immediatly followed by another one. ".\{30,\}\(\n\)" would only match newlines preceeded by at least 30 characters.

Answer 2

If I understand the problem correctly, it is that you would like to preserve all the newlines in the buffer as they are; but you would like to display some of them as spaces. Then, you'd like word-wrapping.

For word-wrapping I think you can use visual-line-mode.

For dealing with the newlines, I think you could perhaps put a display property with " " (a string consisting of a single space) as a value on the newlines you want to display differently.