code: func LeftTrim(str, chars string) string {
  	if chars == "" {
  		return strings.TrimLeftFunc(str, unicode.IsSpace)
  	}
  	r, _ := regexp.Compile("^[" + chars + "]+")
  	return r.ReplaceAllString(str, "")
  }
docs: // LeftTrim trim characters from the left-side of the input.
  // If second argument is empty, it's will be remove leading spaces.