List

list.rb

class List
  attr_accessor :head, :tail

  def initialize(head, tail)
    self.head = head
    self.tail = tail
    freeze
  end

  def prepend(elem)
    List.new(elem, self)
  end

  def append(elem)
    if tail.nil?
      List.new(head, list(elem))
    else
      List.new(head, tail.append(elem))
    end
  end
    
  def inspect
    "(#{head}, #{tail.inspect})"
  end
end

def list(*elements)
  if elements.size == 1
    List.new(elements[0], nil)
  else
    List.new(elements[0], list(*elements[1..-1]))
  end
end

l = list(1, 2, 3, 4)
l = l.prepend(0)
puts l.inspect
l = l.append(5)
puts l.inspect