old_printer

Introduction

The form feed character (aka FF, ASCII 0x0C, Unicode \f, ^L in caret notation) is an artifact from the past.

A past where printers where simpler beasts and relied on a this special invisible (control) character to be told of page breaks.

At a time when people printed their source codes, those characters were commonly used to delimit code sections, forcing a page break for easier reading.

Comments as section delimiters

It’s quite common, especially with programming languages that don’t enforce code segmentation (non OOP-centric) to split a source file in section delimited by comments.

Your typical Python script usually looks something like:

## ------------------------------------------------------------------------
## CONFIG

#[...]


## ------------------------------------------------------------------------
## HELPER FNS

#[...]


## ------------------------------------------------------------------------
## MAIN

#[...]

See all those delimiters made of dashes?

Those lines are generally 75 characters wide to fit under the 80 character width a lot of editors/terminal windows have by default.

This allows displaying the whole line (with no wrap) under most circumstances.

People generally use extensions / keyboard shortcuts to insert those quickly.

But there might be a better way.

Form feed characters as an alternative

Using a line composed of a single FF character instead provides many benefits:

In fact form feed characters can be found in many Clojure, Elisp, C and Python source codes.

Form feed delimiter in Emacs

Emacs’ source code features an extensive use of the FF character.

The output of compilation-mode uses this character (typically when updating several package).

Strangely, by default, Emacs display those characters in caret notation (^L), which is not super user-friendly.

Thankfully, either package form-feed or page-break-lines allows displaying them as a proper horizontal delimiter.

ff_char_emacs

Furthermore, Emacs provides commands to navigate between FF-delimited sections: backward-page (C-x [) and forward-page (C-x ]).

Form feed delimiter in other editors

UltraEdit renders those appropriately natively.

@Alhadis made an package to bring this feature to Atom.

Sadly, nothing seem to exist for IntelliJ IDEA, Sublime Text nor VSCode.

Form feed delimiter on GitHub

GitHub doesn’t style those FF section delimiters.

Thankfully it was trivial to make a userscript to enable this support.

Introducing:

p3r7/gh-userscript-form-feed-line - GitHub

And here is a screenshot of the result:

ff_char_github

The code is small enough to be embedded. The trick is to replace FF lines with <hr/> html elements:

$(document).ready(function(){
    const form_feed=""; // <- there is a FF between these quotes ...
    // ... (even if your web browser doesn't render it)
    $("td.js-file-line:contains('" + form_feed + "')").html('<hr/>');
    $("td.js-file-line > hr").css('margin', '10px auto auto 0');
});

In Conclusion

Using a form feed character as a section delimiter is an elegant solution.

Sadly, few people seem to know about it and few software support it.

So if you want portability, you’d have to stick with the comment-line-made-of-(dashes|underscores|whatever) solution.

If you work on an ecosystem that fully support those, such as Emacs packages, I encourage you to try it.

In any case, it’s sad that “modern” editors don’t support this “old” yet still relevant feature.

But all hope is not lost!

Open issues / PRs. Create plugins/extensions. Spread the word.

See also

Xah Lee’s take on the subject.


Tagged #emacs.