Shoes.app(title: "GUI component interaction") do
  stack do
    textbox = edit_line

    textbox.change do
      textbox.text = textbox.text.gsub(/[^\d]/, '') and alert "Input must be a number!" if textbox.text !~ /^\d*$/
    end

    flow do
      button "Increment" do
        textbox.text = textbox.text.to_i + 1
      end

      button "Random" do
        textbox.text = rand 5000 if confirm "Do you want a random number?"
      end
    end
  end
end