ll.rb

class Node
  attr_accessor :value, :next
  def initialize(value)
    @value = value
  end
end

class LinkedList
  attr_accessor :head, :tail
  def initialize
    @head = @tail = nil
  end

  def add_value(value)
    node = Node.new(value)
    if @head.nil?
      @head = @tail = node
    else
      @tail.next = node
      @tail = node
    end
  end

  def display
    return puts "empty list" if @head.nil?
    current = @head
    while current != @tail
      puts current.value
      current = current.next
    end
    puts current.value
  end
end

ll = LinkedList.new
ll.display
puts "***"
ll.add_value(2)
ll.display
puts "***"
ll.add_value("blah")
ll.display

output

C:\Users\bry>ruby ll.rb
empty list
***
2
***
2
blah