code: def parse_const_argument(lexer: Lexer) -> ArgumentNode:
      
      start = lexer.token
      return ArgumentNode(
          name=parse_name(lexer),
          value=expect_token(lexer, TokenKind.COLON) and parse_const_value(lexer),
          loc=loc(lexer, start),
      )
docs: Argument[Const]: Name : Value[?Const]