code: func (af *aggFunction) String() string {
  	result := af.name + "("
  	for i, arg := range af.Args {
  		result += arg.String()
  		if i+1 != len(af.Args) {
  			result += ", "
  		}
  	}
  	result += ")"
  	return result
  }
docs: // String implements fmt.Stringer interface.