code: def p_ret(p):
      
      if len(p) == 2:
          p[0] = node.expr_list([p[1]])
      elif len(p) == 3:
          p[0] = node.expr_list([])
      elif len(p) == 4:
          assert isinstance(p[2], node.expr_list)
          p[0] = p[2]
      else:
          assert 0
      for ident in p[0]:
          ident.props = "F"
docs: ret : ident
          | LBRACKET RBRACKET
          | LBRACKET expr_list RBRACKET