class Stack {
  constructor(list) {
    this.list = list
  }

  stack() {
    return this.list
  }

  pop(...elms) {
    return new Stack(this.list.concat(elms))
  }

  peek() {
    return this.list[this.list.length - 1]
  }

  pull() {
    return new Stack(this.list.slice(0, this.list.length - 1))
  }
}