Static factorial in clay

fact.clay

procedure fact;
overload fact(static 0) = 1;

[n | n > 0] 
overload fact(static n) = fact(static n - 1) * n;

main() {
  var x = fact(static 4); // == 24, calculated at compile time
}

fact.cpp

template <int N>
struct Factorial 
{
    enum { value = N * Factorial<N - 1>::value };
};
 
template <>
struct Factorial<0> 
{
    enum { value = 1 };
};
 
void foo() {
    int x = Factorial<4>::value; // == 24
}