1class LinkedListStack
 2  def initialize
 3    @head = Node.new(nil)
 4  end
 5
 6  def push(item)
 7    @head.push(item)
 8  end
 9
10  def pop
11    @head.pop
12  end
13
14  def count
15    visitor = TotalCountVisitor.new
16    accept(visitor)
17    visitor.result
18  end
19
20  def accept(visitor)
21    @head.accept(visitor)
22  end
23end
24
25class Node
26  attr_reader :data
27
28  def initialize(data)
29    @data = data
30  end
31
32  def push(item)
33    if @next
34      @next.push(item)
35    else
36      @next = Node.new(item)
37    end
38  end
39
40  def pop
41    if @next
42      if @next.is_tail?
43        result = @next.data
44        @next = nil
45        result
46      else
47        @next.pop
48      end
49    end
50  end
51
52  def accept(visitor)
53    visitor.visit(self) if @data
54    @next.accept(visitor) unless is_tail?
55  end
56
57  def is_tail?
58    @next == nil
59  end
60end