code: func parseQuery(exps []string) ([]*queryObj, error) {
  	queries := make([]*queryObj, len(exps))
  	for idx, exp := range exps {
  		strs := strings.SplitN(exp, ":", 3)
  		if len(strs) != 3 {
  			return nil, errors.Errorf("query expression should be in the form field:op:value")
  		}
  		queries[idx] = newQueryObj(strs[0], strs[1], strs[2])
  	}
  	return queries, nil
  }
docs: // parseQuery parses the input query expressions