Shoes.app :width => 400, :height => 500 do
  rectangles = proc do
    20.times do
      nostroke
      fill rgb((0.6..1.0).rand, (0.1..1.0).rand, (0.2..1.0).rand, (0.4..1.0).rand)
      r = rand(300) + 60
      rect :left => (10..100).rand, :top => (10..200).rand, :width => r, :height => r
    end
    button "OK", :left => 300, :top => 400 do
      clear &rectangles
    end
  end

  rectangles[]
end