my_list.rb

class Node
	attr_writer :data, :index, :next, :prev
	attr_reader :data, :index, :next, :prev
end

class My_list
	attr_reader :node,:total
	
	def add(data)
		
		if @total == nil 
			@total = 1
		else
			@total = @total + 1
		end
		
		if @node == nil
			@parent = Node.new
			@node = Node.new
			@node.data=data
			@node.index = @total-1
			@parent.next = @node
		else
			node = Node.new
			node.data=data
			node.index = @total-1
			
			if @node.next == nil
				node.prev = @node
				@node.next=node
			else
				last_node = @node
				while last_node.next != nil do
					last_node = last_node.next
				end
				last_node.next = node
				node.prev = last_node
			end
		end
		
	end
	
	def each
		node = @parent
		while node.next != nil do
			node = node.next
			yield(node.data)
		end
	end
	
	def find_first
		node = @node
		for i in 0 ... @total do
			value = node.data
			return value if yield(value)
			node = node.next
		end
		return nil
	end
	
	def find
		node = @node
		list = nil
		for i in 0 ... @total do
			value = node.data
			if yield(value)
				list = My_list.new unless list
				list.add(node.data)
			end
			node = node.next
		end
		return list
	end
	
	def inject(n)
		each do |value|
			n = yield(n,value)
		end
		return n
	end
	
	def sum
		inject(0) do |n,value|
			n+value
		end
	end
	
	def product
		inject(1) do |n,value|
			n * value
		end
	end
end