linked_list.rb

require "awesome_print"

module LinkedList
  class Node < Struct.new(:head, :tail)
    undef :head=
    undef :tail=
  end

  def self.unshift(list, el)
    Node.new(el, list)
  end

  def self.shift(list)
    list.tail
  end

  def self.push(list, el)
    case list.tail
    when Node then Node.new(list.head, push(list.tail, el))
    when NilClass then Node.new(list.head, Node.new(el))
    end
  end

  #def pop(list, el)
    #case tail
    #when nil then nil
    #when LinkedList then tail
    #end
  #end
end

class << LinkedList
  def from_ary(ary)
    ary.reverse_each.inject(nil) do |memo, element|
      memo = self::Node.new(element, memo)
    end
  end
end

ap ll = LinkedList.from_ary([1,2,3])
ap LinkedList.unshift ll, 0
ap LinkedList.push ll, 4
ap LinkedList.shift ll