def simple(*args)
      key = args.pop
      on(*args) { |*x| @okay_options[key] = x[0] }
    end
def simple(*args)
      key = args.pop
      on(*args) { |*x| @okay_options[key] = x[0] }
    end
simple(..., :a)
 simple(..., :b)
   ==
 options = {}
 on(...) { |val| options[:a] = val }
 on(...) { |val| options[:b] = val }