code: func ReplaceAtLine(filename string, r []ReplacerAtLine) error {
  	e, err := NewEdit(filename)
  	if err != nil {
  		return err
  	}
  
  	err = e.genReplaceAtLine(r, -1)
  	err2 := e.Close()
  	if err != nil {
  		return err
  	}
  	return err2
  }
docs: // ReplaceAtLine replaces all regular expressions mathed in r for the named
  // file, if the line is matched at the first.