type Stack() {
    var xs = []
}

func Stack.IsEmpty() => this!xs.Length() == 0

func Stack.Peek() => this!xs[this!xs.Length() - 1]

func Stack.Pop() {
    var e = this!xs[this!xs.Length() - 1]
    this!xs.RemoveAt(this!xs.Length() - 1)
    return e
}

func Stack.Push(item) => this!xs.Add(item)

var stack = Stack()
stack.Push(1)
stack.Push(2)
print(stack.Pop())
print(stack.Peek())
stack.Pop()
print(stack.IsEmpty())