# In the Ruby file, foo.rb

class Foo
  def fib(n)
    if (n < 2)
      n
    else
      fib(n - 2) + fib(n - 1)
    end
  end
end


# In the Duby file, foo.duby

class Foo
  method fib
    takes n => Integer::TYPE
    returns Integer::TYPE
  end
end