Compile time recursive objects in c++

Question

I've skimmed this paper today and that's a really cool usage of c++! (At least once you had a look at functional programming languages)
An example, copied from the paper:
template<int N> struct F { enum { val = N * F<N-1>::val }; };
template<> struct F<0> { enum { val = 1 }; };
Do you know more less known cool features of C++? (Of course I'll read and understand the paper first. )

Answer 1

Um...that's the factorial function n! = n * (n-1) *(n-2) [...] * 2 * 1.
After getting my feet wet with functional programming languages, I'm always confused why some things have to be done so difficulty in Cpp. See the corresponding Haskell code:
fac 0 = 1
fac n = n * fac (n-1)
Of course, in cpp it's not nearly as elegant and nice as in Haskell, but it's still better (and at least to me clearer) then the standard recursive approach in cpp (int fact(int n) { if(0 == n) { return 0; } return n * fact(n-1); }), because it won't waste stack space for every function call.
The imperative approach(int temp=1;for (int i=1;i<n;++i) { temp*=i; }) is for this particular function most probably easier, but not every function can be expressed without the use of recursion.
OK, so I'll do further research on template metaprogramming, thanks for the keyword. I have some basic knowledge of templates, but I didn't know this was possible. I'm amazed.