Hammerspoon version of Karabiner's "Control_L to Control_L (+ when you type Control_L only, send escape)"

init.lua

-- Send escape when ctrl is tapped
local send_escape = false
local ctrl_pressed = false

hs.eventtap.new({hs.eventtap.event.types.flagsChanged}, function(event)
  local flags = event:getFlags()
  if flags["ctrl"] then
    ctrl_pressed = true
    send_escape = true
  else
    if ctrl_pressed and send_escape then
      hs.eventtap.keyStroke({}, 'ESCAPE')
    end
    send_escape = false
    ctrl_pressed = false
  end
  return false
end):start()

hs.eventtap.new({hs.eventtap.event.types.keyDown}, function(event)
  send_escape = false
  return false
end):start()