§ 2. The Data Structures

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0. Introduction to the Data Structures
1. Constructor Function: List
2. Constructor Function: Queue
3. Constructor Function: Stack

0. Introduction to the Data Structures

1. Constructor Function: List

   function List() {
     let list = [];
     Object.defineProperty(this, 'length', {
       get: function () { return list.length; }
     });
     this.elementAt = function (i) { return list[i]; };
     this.addAtHead = function (e) { return list.unshift(e); };
     this.addAtTail = function (e) { return list.push(e); };
     this.removeAtHead = function () { return list.shift(); };
     this.removeAtTail = function () { return list.pop(); };
     this.clear = function () {
       const oldList = list;
       list = [];
       return oldList;
     };
     this.forEach = function (f) { return list.forEach(f); };
     this.forSome = function (f, lower, upper) {
       if (lower === undefined) lower = 0;
       if (upper === undefined) upper = list.length;
       for (let i = lower; i < upper; i++) f(list[i]);
     };
   }
   

2. Constructor Function: Queue

   function Queue() {
     const list = new List();
     Object.defineProperty(this, 'length', {
       get: function () { return list.length; }
     });
     this.add = list.addAtTail;
     this.remove = list.removeAtHead;
     this.clear = list.clear;
   }
   

3. Constructor Function: Stack

   function Stack() {
     const list = new List();
     Object.defineProperty(this, 'length', {
       get: function () { return list.length; }
     });
     this.push = list.addAtHead;
     this.pop = list.removeAtHead;
     this.clear = list.clear;
   }