Have you ever done that?

Technique: Compile Time Code Generation and Optimization

by Jonathan Müller

From the article:

C++ constexpr is really powerful. In this blog post, we’ll write a compiler that can parse a Brainfuck program given as string literal, and generate optimized assembly instructions that can then be executed at runtime. The best part: we neither have to actually generate assembly nor optimize anything ourselves! Instead we trick the compiler into doing all the hard work for us.

The same technique can be used whenever you want to specify some sort of “program” in a different way and translate it at runtime: regexes, routing tables, etc.