Turing.rb

class Peano
    def self.method_num
        instance_methods(false)
            .map{ |a| a.to_s}
            .filter{ |a| /\Anum\d+\Z/ =~ a }
            .size
    end
    
    def self.increment
        num = self.method_num + 1
        define_method("num#{num}"){ nil }
    end
    
    def self.decrement
        num = self.method_num
        remove_method("num#{num}")
    end
end

class Tape
    def initalize
        @head = Class.new(Peano)
        @@next_class = nil
        @@prev_class = nil
    end
    
    def increment
        @head.increment
        self
    end
    
    def decrement
        @head.decrement
        self
    end
    
    def next_tape
        if @@next_class.nil?
            @@next_class = Tape.new 
            @@next_class.prev_class = self
        end
        @@next_class
    end
    
    def prev_tape
        if @@prev_class.nil?
            @@prev_class = Tape.new 
            @@prev_class.next_class = self
        end
        @@prev_class
    end
end

Tape.new.next_tape.prev_tape.prev_tape