GSStack

A graph-structured stack.

interface GSStack<T> {
  // Pushes a potentially new node
  // with the given value on top of prev.
  // If prev is undefined, a new stack is created.
  push(value: T, prev?: GSSNode<T>): GSSNode<T>
  // Returns true iff `node` is a top node,
  // meaning it is not a previous node
  // of any other node.
  pop(node: GSSNode<T>): boolean
  // Returns true iff the stack contains no nodes.
  empty(): boolean
}