Are compile-time solutions valid?

Question

I have a couple answers here that work at compile-time and just posted another, and I was wondering if such solutions are allowed. I'm not talking about just proper functions that can run at compile-time, such as constexpr in C++, but also stuff like types that take type parameters and return other types or templates that do something depending on their arguments.

For example, here is a factorial function in Scala 3 using types and some imported black magic:

import compiletime.ops.int._
type Fac[X <: Int] <: Int = X match {
  case 0 => 1
  case _ => X * Fac[X - 1]
}

This does not return a value that can be directly printed. Instead, you would need compiletime.constValue[Fac[6]] to compute the factorial of 6, and not all languages that allow compile-time shenanigans also allow you to turn a type into a value so easily. You might need to verify it using something like val check: Fac[6] = 720 and see if the compiler throws an error or not instead - it's not as simple as just print(factorial(6)).

Are such submissions valid? And if so, what rules do they have to abide by?