code: func ParsePackage(input string) (*Package, error) {
  	stmt, err := ParseStatement(input)
  	if err != nil {
  		return nil, err
  	}
  	pkg, ok := stmt.(*Package)
  	if !ok {
  		return nil, fmt.Errorf("expected package but got %T", stmt)
  	}
  	return pkg, nil
  }
docs: // ParsePackage returns exactly one Package.
  // If multiple statements are parsed, an error is returned.