number-recurssion.rb

module RubyBadgeNumbers
    # Your code goes here...
    class Zero
      attr_reader :pred
  
      def initialize(pred = nil)
        @succ = nil
        @pred = pred
      end
  
      def succ
        @succ ||= PositiveNumber.new(self)
      end
  
      def +(number)
        number.pred ? self.succ + number.pred : self
      end
  
      def -(number)
        number.pred ? self.pred - number.pred : self
      end
    end
  
    class PositiveNumber < Zero

    end
end