Comment by kazinator

The idea behind compile time evaluation is that expressions which are not syntactically constant expressions can also be evaluated at compile time. A function definition can be marked as being available at compile time. When the body of a function f(x) refers to x, that is not a constant expression syntactically. However, an expression like f(3) can be considered a constant expression, since it passes a constant to function that has been marked as a compile-time function.