on fib (n)
  if n<0 then return _player.alert("negative arguments not allowed")

  -- create instance of unnamed class in memory only (does not pollute namespace)
  m = new(#script)
  r = RETURN
  m.scriptText = "on fib (me,n)"&r&"if n<2 then return n"&r&"return me.fib(n-1)+me.fib(n-2)"&r&"end"
  aux = m.script.new()
  m.erase()

  return aux.fib(n)
end