func (s *Stack) Push(tr TokenReader) {
	s.tr = append(s.tr, tr)
}

func (s *Stack) Next() ScanToken {
	tos := s.tr[len(s.tr)-1]
	tok := tos.Next()
	for tok == scanner.EOF && len(s.tr) > 1 {
		tos.Close()
		// Pop the topmost item from the stack and resume with the next one down.
		s.tr = s.tr[:len(s.tr)-1]
		tok = s.Next()
	}
	return tok
}

func (s *Stack) Text() string {
	return s.tr[len(s.tr)-1].Text()
}

func (w *Walker) export(pkg *apiPackage) {
	if verbose {
		log.Println(pkg)
	}
	pop := w.pushScope("pkg " + pkg.Path())
	w.current = pkg
	w.collectDeprecated()
	scope := pkg.Scope()
	for _, name := range scope.Names() {
		if token.IsExported(name) {
			w.emitObj(scope.Lookup(name))
		}
	}
	pop()
}

func set(items []string) map[string]bool {
	s := make(map[string]bool)