gistfile1.ru

def geom_sequence c
  Enumerator.new { |y|
    a = 1
    loop {
      y << a
      a *= c
    }
  }
end

g = geom_sequence 2
p g.take_while{|i| i < 100}
#=>[1, 2, 4, 8, 16, 32, 64]
g = geom_sequence 0.5
p g.take(10)
#=>[1, 0.5, 0.25, 0.125, 0.0625, 0.03125, 0.015625, 0.0078125, 0.00390625, 0.001953125]