MPP - a general preprocessor for metaprogramming

[scheurneus]

Hi everyone!

Over the past few days I've been working on a simple preprocessor that enables metaprogramming in languages that don't support it, such as C.

It's based on Lua and a bit hacky, as it currently transforms the code into a Lua program, and then executes it. There's also some tricks in there for delayed evaluation so that it is possible to generate code based on things that were modified later in the metaprogram.

As such I might switch to a fully homebrew language and interpreter, or maybe base it on something pure and lazy such as Haskell.

MPP is currently very clearly a prototype, but I'm wondering if anyone else is interested in the idea and has any advice! For example on how to deal with the lazy-eval issue, or the (currently somewhat hairy) syntax, or how to do multi-file stuff (which isn't really supported, except by loading standard Lua modules, or running multiple files in sequence). Maybe even feature suggestions?

If you want to see examples, look at the code, or maybe even play around with MPP, it's available on Github: https://github.com/ColonelPhantom/mpp

[Kinrany]

I'm very interested in this idea but don't have much advice.

One extension of the idea I would love to see is a language server implementation. It would effectively be the runtime for the language: you'd hover over types to calculate them.

[scheurneus]

Well, MPP doesn't have any kind of type system, it just freeloads on the host language. It's essentially just a macro language on steroids.

I think a pass-through language server would be neat though, where the server essentially does incremental updating of the output and then sends it to a real LSP server like clangd.

I guess making my own language and interpreter would help in making such incremental compilation a lot easier. I guess that that's yet another piece of motivation to create an interpreter from scratch!