Nfy VS Jinx

For me, the answer is a generic multicast notification system. It utilizes a template based approach that allows you to define prototype messages using a class-based interface that you wish to send to another library. For example, your input library might respond to things like a button down / up, mouse clicks, etc, etc. So you'd create an interface that defines all your input notifications as functions. I won't go into detail, because it's well documented in that link.

In my own code, I make use a generic notification system which allows high-level systems to register themselves with lower-level libraries to help invert dependencies. An example of this is how my game engine's UI library can register itself with the Input library, so it can receive mouse, keyboard, and gamepad events, necessary for manipulating UI controls. But the Game itself also needs to register for some UI events itself, not to mention debug functionality like ImGui for debug windows, etc. So I use this notification system to ensure the low-level Input library can push events out to multiple subscribers without needing to know about them.

See if this is close to what you're looking for: https://github.com/JamesBoer/Nfy

Check out jinx https://jamesboer.github.io/Jinx/

Don't get me wrong, I'm a big fan of automated tests where it makes sense. I wrote a scripting language that I use for my personal game projects, and I never would have been able to do it if it weren't for the battery of tests for every feature, error, and corner case I could think of. But games are rarely like other software, with hard rules about what is "correct" or "incorrect". And it would be a nightmare to try to keep up with designers, constantly tweaking and tuning, so what's "correct" is literally a day to day, constantly moving target.

A second trial for you might be Jinx. Depending on your definition of procedural, Jinx is 100% only procedural. https://jamesboer.github.io/Jinx/

Jinx (embeddable scripting language) works as following:

Feel free to look at my own interpreter, written in modern C++. You're welcome to ask me if you have any questions.

I use my own scripting language more like content, especially for things like one-off events and behaviors. Example: scripting special behaviors for a boss fight, or a room with a unique trap in it, or any other sort of one-off behavior that would be overkill for C++, but too complex for most other types of data-driven content. These days, visual scripting also helps to fill in these gaps between content and procedure.

You're welcome to look at my scripting language Jinx, written in modern C++. Just let me know if you have specific questions. Data flow is JxLexer.cpp -> JxParser.cpp -> JxScript.cpp. Most everything else is implementation details. Also, note the parer is pretty complex, mostly because Jinx has a crazily flexible syntax for functions.

Feel free to look at Jinx if you want an example of what I consider a fairly easy-to-use and integrate scripting system. Obviously, I'm a bit biased since I wrote it.

If you're working in UTF-8 internally, you could just write your own UTF-16 to UTF-8 conversion functions to convert strings at API boundaries. I did this in my scripting language because I didn't want to bring in dependencies.