def to_h
      ret = Hash.new
      @list.each do |i|
        ret[i.car.to_ruby] = i.cdr.to_ruby
      end
      ret
    end
def to_h
      ret = Hash.new
      @list.each do |i|
        ret[i.car.to_ruby] = i.cdr.to_ruby
      end
      ret
    end
alist -> hash