The stack from my Pry screencast

stack.rb

# The stack I wrote for http://vimeo.com/26391171
# Note that there is an intentional bug in the each method :)

class Stack
  
  Node = Struct.new :data, :next
  
  def push(data)
    @head = Node.new data, @head
  end

  def pop
    return unless @head
    data = @head.data
    @head = @head.next
    data
  end

  ##
  # Iterates across the stack
  # 
  #   stack = Stack.new
  #   stack.push 5
  #   stack.push "abc"
  #   array = []
  #   stack.each { |element| array << element }
  #   array # => ["abc", 5]
  def each
    crnt = @head
    loop do
      yield crnt.data
      crnt = crnt.next
    end
  end
end