parser/symbols.go
func (s LexSymbolSorter) Swap(i, j int) {
	s.list[i], s.list[j] = s.list[j], s.list[i]
}
func (s LexSymbolSorter) Swap(i, j int) {
	s.list[i], s.list[j] = s.list[j], s.list[i]
}
// Swap swaps the elements at i and j