I wrote PCCL for a use case like this: mostly config but with dynamic behavior. I've also used Lua in the same way. My favorite memory of this approach was when some vendor switched from a static configuration to a daily XML config on their FTP site. I modified our config file so instead of hard coding the vendor's old parameters, it would download their XML file and populate our config params such that the C++ host program did not know anything had changed.

Some people say a Turing complete config language is a step too far. With great power....

https://github.com/jzwinck/pccl