code: func parseEnumValueDefinition(parser *Parser) (interface{}, error) {
  	start := parser.Token.Start
  	description, err := parseDescription(parser)
  	if err != nil {
  		return nil, err
  	}
  	name, err := parseName(parser)
  	if err != nil {
  		return nil, err
  	}
  	directives, err := parseDirectives(parser)
  	if err != nil {
  		return nil, err
  	}
  	return ast.NewEnumValueDefinition(&ast.EnumValueDefinition{
  		Name:        name,
  		Description: description,
  		Directives:  directives,
  		Loc:         loc(parser, start),
  	}), nil
  }
docs: /**
   * EnumValueDefinition : Description? EnumValue Directives?
   *
   * EnumValue : Name
   */