datatype99 VS epilepsy

Sum types and pattern matching have already been hacked together in a preprocessor macro in C; see https://github.com/Hirrolot/datatype99.

It does not. There are people who have implemented such constructs in C code however, for example: https://github.com/Hirrolot/datatype99

Nice reference but with some strange bits:

> Algebraic data types are usually represented using a heap. Because of their non-uniformity, algebraic data types are more difficult to scan.

Using a heap??? We can represent ADTs using stack as well, that's what we usually do in C and Rust.

Shameless plug: https://github.com/Hirrolot/datatype99 (a library of mine that generates type-safe ADTs for pure C99).

I agree; I would especially not recommend abusing macros throughout an application codebase too much. Conceptually, Metalang99 is more of a (sub)language than a library, which also adds some entry barrier. Ideally, I see the application of Metalang99 being used "behind the scenes", e.g., encapsulated in separate code files/libraries such as Datatype99 and Interface99. This is what I (mostly) do in SmolRTSP.

I've done something similar with Datatype99 and Interface99. They are like a macro eDSL that compiles to C. The first one features algebraic data types, the second one features interfaces.

If you need a bit more high-level constructions, you can use the Datatype99 and Interface99 libraries. The former provides polymorphism over data, the latter -- over behaviour (I am the creator of these libraries).

OP, you might find datatype99 and its sibling projects interesting, though they mostly leverage the C preprocessor without going all the way towards defining a new language.

You can use Datatype99 to represent your AST tagged union conveniently.

Compared to plain C, you have ADTs which help from day to day programming. You can bring them to C (https://github.com/Hirrolot/datatype99) but I don't know if the Linux guys would allow it.

Yes, as others have already noticed, it is implemented on top of https://github.com/Hirrolot/epilepsy, a metalanguage for preprocessor metaprogramming.