Naive implement n/1 enumerator.

reciprocal.rb

class Reciprocal
  include Enumerable

  def initialize(i)
    @denon = i
  end
  def each
    numer = 1
    nums = []
    loop do
      q,r = numer.divmod(@denon)
      if (q == 0 && (nums.all?(0) || nums.empty?)) || q != 0
        nums << q 
        yield q
      end
      if q == 0
        numer *= 10
        redo
      end
      break if r == 0
      numer = r
    end
    return nums
  end
end

Class of pure implementation of reciprocal numbers.
It's enumerable.
You can get never ending numbers if you want.

ruby -e 'p Reciprocal.new(7).to_enum.take(100)'
[0, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7,1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8, 5, 7, 1, 4, 2, 8]

Benchmark

Benchmark.bm do |bm|
  bm.report { Reciprocal.new(7).to_enum.take(1000) }
  bm.report { Reciprocal.new(7).to_enum.take(10000) }
  bm.report { Reciprocal.new(7).to_enum.take(100000) }
  bm.report { Reciprocal.new(7).to_enum.take(1000000) }
  bm.report { Reciprocal.new(7).to_enum.take(10000000) }
end

       user     system      total        real
   0.001078   0.000066   0.001144 (  0.001136)
   0.012444   0.000422   0.012866 (  0.014372)
   0.087633   0.002223   0.089856 (  0.093306)
   0.832047   0.014849   0.846896 (  0.859842)
   8.623119   0.231629   8.854748 (  9.931088)

思ったより速い。