title: Corona "tick" issues - addEventListener
body: <p>I've been trying to write out a custom tick using the Corona SDK (using Lua).  The key seems to be these "eventListeners," but I'm also trying to get them to work with classes.  right now i have this class "World" set up.  I'm trying to add an EventListener to my "tick" function, but Corona is telling me I can't do it.</p>
  
  <pre><code>function World:tick()
  --player:tick()
  --camera:tick(player.x,player.y)
  --for i=0,monsters.length do
  --      monster[i]:tick()
      if(rwalk) then
          mainGroup.x = mainGroup.x-10
      elseif(lwalk) then
          mainGroup.x = mainGroup.x+10
      end
  end
  Runtime:addEventListener("enterFrame",tick)
  </code></pre>
  
  <p>Error: Runtime error: assertion failed!
  stack traceback:
          [C]: ?
          [C]: in function 'assert'
          ?: in function 'getOrCreateTable'
          ?: in function 'addEventListener'
          ?: in function 'addEventListener'
          C:\Users\Evan\Desktop\lua\test game\main.lua:337: in main chunk</p>