Define extended keyboard layer on Mac using Karabina-elements and Goku

As a Vim user, I often find it annoying to switch between normal mode and insert mode for minor edits. For example,

cursor location `\|`	todo	escaping	single key
`abc\|`	delete c	`<esc> + s`	`backspace`
`abc\|d`	delete d	`<esc> + l + s`	`delete_forward`
`abc\|`	go to beginning of line	`<esc> + I`	`home`
`{abc\|}`	move cursor to the right of `}`	`<esc> + A`	`right_arrow`

You can see it’s more key presses using the escaping approach. On the other hand, these single keys are located far away.

The ideal solution is to define another keyboard layer with these useful keys mapped at some easily accessible locations. This is a common practice in the custom keyboard community. Such a layer is called the extended layer, and the mapping is almost standardized.

For example, the following layer comes from the Ergonomic Keyboard Mods site. extend-layer

The main change is under the right hand

page_up	home	up_arrow	end
page_down	left_arrow	down_arrow	right_arrow	delete_forward

As shown in the image, the typical triggering key is either the capslock or the key left to the spacebar. For example, <trigger> + k gives rise to down_arrow, where k refers to the key under the right middle finger at rest position. Since my capslock key is already been used for escape, I use left command key for triggering.

The following layer comes from DreymaR on the colemak forum. You may also be interested in his Big Bag of Keyboard Tricks. extend-layer-DreymaP

set up on MacBook Pro

Such an extended layer is easy to set up on a programmable keyboard. Recently I realized that it can be done on MacBook Pro (probably other Mac machines too) using two software

Karabiner-Elements: it modifies keys
Goku: it is a DSL (domain specific language) to help define key combos for Karabiner-Elements

Their installations are straight forward. Just remember to allow karabiner_grabber and karabiner_observer in System Preferences -> Security & Privacy -> Input Monitoring. Also make sure there is a Default profile in Karabiner-Elements -> Profiles.

Then place the following content in ~/.config/karabiner.edn.

{:main [{:des "extended layer with left command",
     :rules [
            [:!Cj :left_arrow]
            [:!Ck :down_arrow]
            [:!Ci :up_arrow]
            [:!Cl :right_arrow]
            [:!Cu :home]
            [:!Co :end]
            [:!Ch :page_down]
            [:!Cy :page_up]
            [:!Csemicolon :delete_or_backspace]
            [:!Cspacebar :delete_forward]
      ]}]
 }

Here C is the left command key. ! means the command key press is mandatory.

Note that even if you use a different keyboard layout from qwerty (I use colemak-dh), this is still the correct content.

With this karabiner.edn in place, type in shell

goku

If all goes well, you will see

Done!

And ~/.config/karabiner/karabiner.json will be updated. Also Karabiner-Elements -> Complex modifications will show extended layer with left command.