gistfile1.rb

get '/sqrt/:num.:format' do
  model = Math.sqrt(params[:num].to_f)
  content_type params[:format].to_sym
  format(model, params, self)
end

def format(model, params, app)
  if %w{xml json pdf xls csv html}.include? params[:format]
    app.send(params[:format], model)
  else
    model.inspect
  end
end