vm/state.go
func (st *State) CurrentMark() int {
	x, err := st.markstack.Top()
	if err != nil {
		x = 0
	}
	return x.(int)
}
func (st *State) CurrentMark() int {
	x, err := st.markstack.Top()
	if err != nil {
		x = 0
	}
	return x.(int)
}
// CurrentMark returns the mark stored at the top of the mark stack