Very basic, probably bad in some way gamestate module

gamestates.lua

local gamestates = {}
gamestates.debug = false

function gamestates:init (initialstate)
  self.stack = {}
  self.num = 0
  self:clear(initialstate)
end

function gamestates:update (dt)
  assert(self.num > 0, "The state stack is empty.")
  self.stack[self.num]:update(dt)
  -- debug
  if imgui and self.debug then
    imgui.SetNextWindowPos(50, 50, "FirstUseEver")
    imguistatus, self.debug = imgui.Begin("Gamestates", true, {"AlwaysAutoResize"});
    imgui.Text("States in stack: "..self.num)
    for i=self.num,1,-1 do
      imguistatus, self.stack[i].debug = imgui.Checkbox(self.stack[self.num].state, self.stack[i].debug)
    end
    imgui.End()
  end
end

function gamestates:draw ()
  assert(self.num > 0, "The state stack is empty.")
  self.stack[self.num]:draw()
end

function gamestates:keypressed (...)
  assert(self.num > 0, "The state stack is empty.")
  if self.stack[self.num].keypressed then
    self.stack[self.num]:keypressed(...)
  end
end

function gamestates:push (state, ...)
  assert(state, "Tried to push a falsy state.")
  if self.stack[self.num].pause then
    self.stack[self.num]:pause(state)
  end
  if state.enter then
    state:enter(self.stack[self.num], ...)
  end
  self.num = self.num+1
  self.stack[self.num] = state
end

function gamestates:pop ()
  assert(self.num > 1, "Tried to pop the final state.")
  local previous = self.stack[self.num]
  self.stack[self.num] = nil
  self.num = self.num-1
  if previous.exit then
    previous:exit(self.stack[self.num])
  end
  if self.stack[self.num].resume then
    self.stack[self.num]:resume(previous)
  end
  return previous
end

function gamestates:clear (newstate, ...)
  assert(newstate, "Tried to clear the stack to a falsy state.")
  local previous
  for i=self.num,1,-1 do
    self.stack[i]:exit()
    previous = self.stack[i]
    self.stack[i] = nil
    if i ~= 1 then
      self.stack[i-1]:resume(previous)
    end
  end
  self.stack = {newstate}
  self.num = 1
  if self.stack[1].enter then
    self.stack[1]:enter(nil, ...)
  end
end

return gamestates