[Ur] Looking for an example of a common pattern

[Adam Chlipala]

On 04/19/2013 10:25 PM, David Snider wrote:
> There is a common pattern in web development of redirecting a user to 
> a login page when their login cookie can not be found. If the login is 
> invalid it regenerates the page with an error message, otherwise it 
> generates the requested page. Could someone show me an example of how 
> to use a functor to generate this functionality for any page?

It's not obvious that there's any particular reason to use a functor here.

> I tried this myself and ran into issues like having the Login and 
> HomePage module be mutually dependent on each other. I am not sure 
> what the correct way to do this is.

For mutual recursion across modules, I use URLs built by reference to 
string paths directly.  It forfeits some of the nice static guarantees 
of Ur/Web, but it's not obvious to me what the right alternate language 
feature would be.