Boon: An Ergonomic Command Mode for Emacs

Boon is a complete package for modal editing, which is not Evil.

Strong points:

• Ergonomic: common commands are easy to type.
• Emacs-friendly: Emacs conventions are respected as much as compatible with design goals. This means that Boon integrates well with existing Emacs infrastructure, and leverages it. Existing user configuration can often be re-used.
• Modular: No need to buy into the whole system: mix-and-match the parts you want.

Ergonomic Design

It is largely accepted that modal editing is more ergonomic than using key-chords. Boon attempts to take this advantage to its conclusion, making modal editing as comfortable as possible, by adhering to the following design principles:

• Spacial allocation first, mnemonics second: the allocation of keys to commands is primarily based on the locations of keys on the keyboard. Whatever is printed on the key cap is a secondary concern.

• Easy finger rolls: common key combinations should either be left/right hand alternation or easy one-hand rolls.

• Use of home row and strong fingers for the most used commands.

• Easy navigation: many keys are allocated to navigation. This strategy facilitates moving around, which is in fact the most common task when editing text. Because movements double up as region-definitions, this design also makes manipulation commands more powerful.

• Prefer an easy two-keystroke combination to a single hard-to-reach key. Hard-to-reach keys are free for the user to bind to rarely used commands (often user and mode-dependenent).

In command mode, movement keys are bound to the right hand, while text manipulation is bound to the left hand. This division of tasks is reminiscent of game-console controllers.

Right-hand.

The leftwards (and upwards) movements are bound to the leftmost fingers (index and middle finger), while rightwards (and downwards) movements are bound to the rightmost fingers (ring finger and pinky.) Additional unpaired movements are bound to the middle column, which is reached with an extension of the index finger.

Left-hand.

The most common editing commands (cut, paste, parenthesis manipulation) are bound to the home row. The top row is (mainly) for searching. The bottom row gives access to user-defined (C-x) and mode-specific shortcuts (C-c), insert mode, and registers.

Emacs integration

1. C-x and C-c shortcuts. Any 'C-x ' command is available via 'x '. (drop the 1st "Control"). Thus 'x s' will save all buffers, etc. C-c C- shortcuts are now typed simply as "c ". This means that no special configuration is required when you start using a new major or minor mode.

2. 'Special' modes. Emacs already has several modes which have a modal interface. (Dired, Magit, etc.) Instead of re-inventing the wheel, Boon leaves these modes alone (mostly). Only the 'x' key is stolen by Boon (so splitting windows, switching buffers, etc. keep their usual shortcut.)

3. Command repeats. Boon does not use its own mechanism to repeat commands: it simply uses the Emacs standard way. Commands which contain an insertion (eg. replace current word by something else) are properly recorded in Emacs command history. Emacs command history remains fully usable with Boon.

4. Parsing commands. Boon does not have a special way to parse commands. Everything is done using Emacs keymaps and interactive arguments.

5. Customize-friendly. Quick customization is easily done using M-x customize-group boon. (re)-Defining keys in the boon-...-keymaps is also supported.

6. Multiple-cursors support. System of selectors supports multiple-cursors: (multiple regions will be returned when multiple cursors are active).

Modular design

Boon is designed as set of modules, largely independent of each other. Each module is customizable and provides reusable components, in following the Emacs spirit of hackability. This means that even if you disagree with the design choices explained above, you may still want to use some parts of Boon. The structure of Boon is as follows:

1. boon-moves.el and boon-search.el provide a set of move and search commands. These work the same way as standard Emacs commands --- they are merely more powerful (or just have different emphasis). Layout-frontends typically bind these commands (in addition to standard ones) in the boon keymaps.
2. boon-arguments.el provides a set of selectors to define regions. (These selectors are the equivalent of vim 'text objects'). Selectors include plain regions (words, lines, paragraphs, ...), but also region transformers (think: exclude borders, just borders, including spaces, "foreach", etc.). Additionally every move command (in the boon-moves-map keymap) can be used as a selector which means that they are easily customized.
3. boon-core.el provides an infrastructure for modal editing. The implementation draws much inspiration from evil-core, but is heavily simplified.
4. boon-main.el provides a set of commands. These are similar to standard Emacs commands, but they use the system of selectors described above. (For good measure, some random extra commands are thrown in.) These commands may be used in combination with a modal system or not. A few commands also switch to insert mode.
5. boon-keys.el, boon-colemak.el, boon-qwerty.el, etc. are (layout-specific) frontends. Those require all the above and provide a mapping of moves, selectors and commands onto keys.

Installation

REQUIREMENTS

• Emacs version >= 25.1
• Qwerty, Qwertz or Colemak layout (Workman version partially implemented -- contributions welcome).

Install Boon (perhaps using ), and add the following to your configuration:

(require 'boon-colemak)
;; (require 'boon-qwerty) ;; for qwerty variant

Then

(boon-mode) ;; to enable boon everywhere

If you just eval'ed the above (or just did not want to enable boon everywhere), Boon may not be active in the current buffer. If it is not activated and you want to try it locally, activate it by

M-x turn-on-boon-mode

Usage

You can jump-start by reading any of the cheat sheets (colemak, qwerty) directly, but reading through the tutorial is highly recommended:

(require 'boon-tutorial)
M-x boon-tutorial

(You'll get the version of the tutorial adapted to the layout-frontend you have activated, qwerty, colemak, etc.)

Configuration

The main variables to configure are:

• boon-select-map, boon-moves-map, boon-command-map, boon-insert-map, boon-special-map. (Those are keymaps.)

• boon-enclosures (can be customized.)

If you use powerline (or mutatis mutandis spaceline), you may want to:

(require 'boon-powerline)
(boon-powerline-theme) ;; if you want use powerline with Boon

• Per-mode keybinding can be implemented by setting the boon-map property of the mode symbol. Example:

  (let ((map (make-sparse-keymap))) (set-keymap-parent map boon-command-map) (define-key map "j" 'org-open-at-point-global) (put 'org-mode 'boon-map map))

Comparison with other modal layers for Emacs

If possible I would have liked not to develop Boon (or parts of it) and use an existing package. Hence I have looked into other options and have documented my research below. In summary, even though I would like to share code and/or replace parts of Boon with similar package, at the moment no package offers enough that I feel the urge to try and use them. This is partly due to the fact that Boon maintenance burden is fairly low. (And at the time of inception, the only conceivable alternative was Evil.)

• Evil

  Evil is a (quite) complete vi emulation layer for Emacs.

  In contrast, in Boon, much of Emacs structure is leveraged and user experience is retained. Examples: the x key gives the C-x prefix map. The usual Emacs (interactive) arguments are used for text objects. Thus most of Boon remains usable even if one does not wish to use modal editing.

  Besides, the vi keybindings do not provide the best ergonomics (IMO).

  Making a boon-like layer on top of Evil appears theoretically possible, but I judge that the amount of work to gain an understanding of the code such that this would be practical would require more work than using Boon separately. Additionally, Emacs integration would still be poorer.

• Xah Fly Keys http://ergoemacs.org/misc/ergoemacs_vi_mode.html

  Like boon, Xah Fly Keys (hereafter abbreviated to XFK) aims at providing a layout whose design is ergonomic. (According to the author it constitutes "the most efficient editing system in the universe".) Regardless, there follows a comparison based on my understanding.

  1. As far as I can tell XFK has no notion of selectors (vim's ``text objects''). Instead some keys are specially purposed to delete specific chunks of texts. Boon has a smaller set of useful commands and modifiers which can be combined in useful ways. It leaves keys for more "clever" navigation commands (eg. browsing errors) and editing shortcuts (eg. replace and insert in one keystroke).

  2. XFK binds digits to actions, boon leaves them for prefixes. (I may be misunderstanding here --- perhaps they are bound to special characters.)

  3. XFK seem to have less of a systematic assignment of keys to actions, even though the movements are roughly bound to the right hand. I believe that a more systematic binding startegy is easier to learn.

  4. Boon provides 1-key access to C-x and C-c prefixes. Instead, XFK puts everything under a single "leader key" (space), presumably without preserving emacs convention.

  5. The set of supported layouts is different. (Even though I'd expect ports to be easy.) As far as I can see, XFK has an automatic way to construct maps for a new keyboard layout. This is a worthy idea, but unfortunately boon already uses ad-hoc mapping depending on the layout, so adopting this strategy is not backwards compatible.

• Fingers https://github.com/fgeller/fingers.el

  Fingers borrows a few ideas from Boon, including the division of work between left and right hand. The author (fgeller) gives a detailed account of the particular differences with Boon. My opinion is that Fingers is compatible with Boon concepts and could (and probably should) be implemented as a Boon layout-frontend.

• Modalka https://github.com/mrkkrp/modalka

  Modalka is an engine to "introduce native modal editing of your own design". Thus its purpose is similar to boon-core.el. It could be possible and beneficial in the future to replace parts of boon-core with a dependency on Modalka. However at the moment it does not seem suitable. The main issue is that modalka does not support several states; it can only be either activated or not. Also, this part of Boon is sufficently simple that adding a dependency may be more troublesome than helpful.

• RYO modal mode https://github.com/Kungsgeten/ryo-modal

  RYO modal has the same purpose as Modalka and boon-core; it is also a candidate to replace boon-core.el, but still falls short. Compared to Modalka, it provides support for repeating a command. However boon can repeat insertion commands, while RYO modal cannot. Additionally it also suffers from having a single non-insertion state.

• God-mode https://github.com/chrisdone/god-mode

  God-mode is similar to "sticky modifier keys" in principle. Its simplicity allows to quickly get up to speed with it. However, it lacks the main benefit of a true modal layer: text operators. (what vi people call a "language for text editing"). Boon integrates god-mode functionality for the C-c prefix map specifically (bound to the c key).

• Modal Mode http://retroj.net/modal-mode (Last updated in 2014)

  Another modal layer for Emacs, which is also lightweight and aims to integrate with Emacs. However, as far as I can see, there is no special attention paid to ergonomics.