code: def p_GlobalVaribleList(p):
      '''
      GlobalVaribleList : Varible 
                        | GlobalVaribleList COMMA Varible
      '''
      if len(p) > 2:
          p[0] = GlobalVaribleList(p[1], p[3])
      else:
          p[0] = GlobalVaribleList(None, p[1]f p_GlobalVaribleList(p):
      '''
      GlobalVaribleList : Varible 
                        | GlobalVaribleList COMMA Varible
      '''
      if len(p) > 2:
          p[0] = GlobalVaribleList(p[1], p[3])
      else:
          p[0] = GlobalVaribleList(None, p[1])
docs: GlobalVaribleList : Varible 
                        | GlobalVaribleList COMMA Varible