// Following implemetation of Stack tie each element to it parent
type stackElement struct {
	data interface{}

	next *stackElement
}

type Stack struct {
	Size int32
	head *stackElement
}

func (stack *Stack) Push(data interface{}) {
	element := new(stackElement)
	element.data = data
	element.next = stack.head
	stack.head = element
	stack.Size++
}

func (stack *Stack) Pop() interface{} {
	if stack.head == nil {
		return nil
	}

	v := stack.head.data
	stack.head  = stack.head.next
	stack.Size--

	return v
}

func (stack *Stack) IsEmpty() bool {
	return stack.head == nil
}