-- https://pastebin.com/D8yWJ7rh
function newManager(side)
  local manager = {
    buttons = {},
    monitor = peripheral.wrap(side),
    newButton = function(self, label)
      print("creating button ''"..label.."''")
      self.buttons[label] = {
        label = label,
        text = "_ "..label
      }
    end,
    draw = function(self)
      print("starting draw()")
      self.monitor.clear()
      self.monitor.setCursorPos(1,2)
      local yPos = 2
      for button in self.buttons do
        self.monitor.write(button.text)
        yPos = yPos + 1
        self.monitor.setCursorPos(1,yPos)
      end
    end
  }
  return manager
end

local mgr = newManager("top")
mgr:newButton("Iron")
mgr:newButton("Dye")
mgr:newButton("Coal")
mgr:draw()