code: func toBit(l yyLexer, lval *yySymType, str string) int {
  	b, err := types.ParseBit(str, -1)
  	if err != nil {
  		l.Errorf("bit literal: %v", err)
  		return int(unicode.ReplacementChar)
  	}
  	lval.item = b
  	return bitLit
  }
docs: // See https://dev.mysql.com/doc/refman/5.7/en/bit-type.html