Mutually recursive template expansion

[Stephen via Digitalmars-d-learn]

I've been trying out templates in more depth and one thing I was 
wondering was whether template expansions with circular 
dependencies might work.
Here is an example that doesn't work:
```d
mixin(A!());
mixin(B!());
void main() {}

template A() {
    const char[] A = q{
        struct Ar {
            Br b;
        }
    };
}

template B() {
    const char[] B = q{
        struct Br {
            Ar a;
        }
    };
}
```
This code should work should mutual recursion be supported. How 
might I get it to work properly (without sacrificing recursion or 
templates)?