design
  cons module Toggle
    cons input toggle 1 nil
    cons state q 1 false
    cons next q xor q toggle
    nil
    cons output value 1 q nil
  nil
  Toggle
  cons test sequence Toggle
    cons tick cons true nil cons false nil
    cons tick cons true nil cons true nil
    cons tick cons false nil cons false nil
    cons tick cons false nil cons false nil
    nil
  nil