public class Stack[T]
{
    private stack : list[T];

    public this()
    {
        stack = [];
    }

    public this(init : list[T])
    {
        stack = init;
    }

    public Push(item : T) : Stack[T]
    {
        Stack(item::stack)
    }

    public Pop() : T * Stack[T]
    {
        (stack.Head, Stack(stack.Tail))
    }

    public Peek() : T
    {
        stack.Head
    }

    public IsEmpty() : bool
    {
        stack.Length == 0
    }
}