Cnx VS metalang99

The biggest obstacles to make some form of functional programming (think more like Rust than Haskell) possible are __VA_OPT__, auto, lambdas, and defer. IIRC the first two are coming in C23. The last two might make it into the next standard after that, but unlikely to make 23. If you're willing to limit yourself to GNU C (so compiling with GCC or Clang, or maybe ICC) you can get pretty close already today. (shameless self plug) My project Cnx (https://github.com/braxtons12/Cnx) attempts to bring a more modern approach to the language, and a big chunk of the features it implements are functional in nature.

There are also other approaches. Macro variants making use of `__VA_ARGS__` would be probably the best trade-off. If you want a slightly more ergonomic syntax, something like Metalang99 [1] will help (and the author even wrote a post about this exact subject [2]). Codegen is another option which may work better than other options depending on the situation and exact implementation strategy. And there is always the Reflection TS [3], which may or may not be incorporated to C++26...

[1] https://github.com/Hirrolot/metalang99

[2] https://hirrolot.github.io/posts/pretty-printable-enumeratio...

[3] https://en.cppreference.com/w/cpp/experimental/reflect

I went down the rabbit hole with C99 metaprogramming after reading through the list. For reference: https://metalang99.readthedocs.io/en/latest/, https://github.com/Hirrolot/metalang99

Honestly I have to disagree. There is nothing particularly special about what Super Template Tetris(STT) is doing.

At its core, template metaprogramming is just functional programming at compile time. STT is just a template and a runtime function which do the following:

1, take an input via compile time flag (the `-D DIRECTION`)

2. take a type input from an included header file containing the current state (`#include "current_game.h"`)

3. via functional programming, compute the results of a single step of the game.

4. specialise a single function using the results of step 3. this function prints the computed result to the screen and the computed game state to a file (`./current_game.h`).

5. gcc/clang exits. compilation is complete.

6. call the compiled binary.

7. the binary runs the specialised function and prints the outputs.

Sure it's fucky and you shouldn't do that in production but what sane individual is writing a piece of code that at runtime (after compiling) seeks out one of its own source files and modifies that file?

To prevent this from being possible you'd have to remove runtime file IO from the language. The other potential solutions wouldn't work:

1. Remove templates entirely: Still would be possible using https://github.com/Hirrolot/metalang99 which solely uses the preprocessor. Given that the pre-processor is literally just term substitution(a glorified copy/paste engine), if you removed that as well, you'd have to accept no form of metaprogramming at all.

2. Remove the ability to #include other files: Could still be done by doing everything inline. `#include` is just copy-paste anyways so it's more an abstraction than anything else to the compiler and preprocessor, it's basically the same as if all the code was pasted into the same file.

That leaves you with removing file IO. Without IO a programming language is basically useless, particularly as a systems programming language.

P.S. I wrote Metalang99 BTW.

Metalang99, a metalanguage for C99. Simple :)

Just wait until you see some other things by the same author, like https://github.com/Hirrolot/metalang99

I did get a few great responses there as well, though. One was a link to this impressive piece of work: https://github.com/Hirrolot/metalang99/blob/master/examples/lambda_calculus.c

Some preprocessor nonsense: https://github.com/Hirrolot/metalang99/blob/master/examples/lambda_calculus.c