Remapping caps-lock with kmonad

macbookpro.kbd

(defcfg

;; Of course we want fall-through. What would be the point of not having fall-through.
fallthrough true  

;; JESUS CHRIST no. We are not having the keyboard directly executing commands.
allow-cmd false

;; This is the keyboard we're reading from...
input  (device-file "/dev/input/by-id/usb-Apple_Inc._Apple_Internal_Keyboard___Trackpad_D3H5141GLZ1GHJGA71KF-if01-event-kbd")

;; And this is the virtual keyboard we're writing to. Name doesn't really matter.
output (uinput-sink "My KMonad output")

)

(defsrc

;; The keyboard before modification. Some keys (function keys, cursors, bspc) generate
;; different keycodes when fn is held, they're positioned close to the key. I think we
;; can actually turn off the special behaviour of the fn-key and take control of it
;; ourselves, using /sys/module/hid_apple/parameters/fnmode but let's worry about that
;; another day.

                 brdn   brup   scale  dashboard bldn blup  prev playpause next  mute   vold   volu
  esc            f1     f2     f3     f4     f5     f6     f7     f8     f9     f10    f11    f12    power
  `              1      2      3      4      5      6      7      8      9      0      -      =      bspc   del
  tab            q      w      e      r      t      y      u      i      o      p      [      ]
  caps           a      s      d      f      g      h      j      k      l      ;      '      \      ret
  lsft    102d   z      x      c      v      b      n      m      ,      .      /                    rsft
  fn      lctl   lmet   lalt                 spc                         rmet   ralt   left   down   up     right
                                                                                       home   pgdn   pgup   end
)


(defalias

;; Caps-escape acts as escape if tapped for <200ms, otherwise as a modifier to access the "holdcesc" layer.
cesc (tap-hold 200 esc (layer-toggle holdcesc))

)

;; Default key behaviours.
(deflayer default
                 brdn   brup   scale  dashboard bldn blup  prev playpause next  mute   vold   volu
  esc            f1     f2     f3     f4     f5     f6     f7     f8     f9     f10    f11    f12    power
  `              1      2      3      4      5      6      7      8      9      0      -      =      bspc   del
  tab            q      w      e      r      t      y      u      i      o      p      [      ]
  @cesc          a      s      d      f      g      h      j      k      l      ;      '      \      ret
  lsft    102d   z      x      c      v      b      n      m      ,      .      /                    rsft
  fn      lctl   lmet   lalt                 spc                         rmet   ralt   left   down   up     right
                                                                                       home   pgdn   pgup   end
)

;; Key behaviours when caps-escape is held. Underscores fall-through to the default layer.
(deflayer holdcesc
                 _      _      _      _      _      _      _      _      _      _      _      _
  _              _      _      _      _      _      _      _      _      _      _      _      _      _
  esc            _      _      _      _      _      _      _      _      _      _      _      _      del    _
  caps           _      _      _      _      _      _      _      ins    _      prnt   _      _
  _              _      _      _      _      _      left   down   up     right  _      _      _      _  
  _       _      C-z    C-x    C-c    C-v    _      _      _      _      _      _                    _
  _       _      _      _                    _                           _      _      _      _      _      _
                                                                                       _      _      _      _
)

I put this at /etc/kmonad/macbookpro.kbd and did

sudo systemctl start kmonad@macbookpro
sudo systemctl enable kmonad@macbookpro

This works because the Arch package has created /usr/lib/systemd/system/kmonad\@.service with this definition:

[Unit]
Description=KMonad keyboard config

[Service]
Restart=always
RestartSec=3
ExecStart=/usr/bin/kmonad %E/kmonad/%i.kbd
Nice=-20

[Install]
DefaultInstance=config
WantedBy=default.target

The %E means /etc and the %i means "whatever you put after kmonad@ when invoking systemctl.