[gsliepen]

> Could anyone explain to me how this is different from templates or parameter pack expansion in C++?

I don't think it's any different.

> I can see the constexpr-ness here is encoded in the type system

I also see they introduce new constructs like let$, so it's not just a type system thing.

> I looked at the paper but I can't find anything related to C++.

I don't think the author needs to compare their code to C++. That said, it looks to me like it is similar to the upcoming C++26's reflection capabilities.

[naasking]

Typically, multistage languages permit program generation at any stage, including runtime. So that would be different than C++.

[gsliepen]

You can get pretty far in C++ though: https://codereview.stackexchange.com/questions/259045/poor-m...

[naasking]

This looks like a reinvention of the final, tagless interpreter, which has been a great, common technique in functional languages for awhile:

https://okmij.org/ftp/tagless-final/index.html#tagless-final

It's an interpreter though, not a JIT. This kind of programming language thing is a bit of a hobby horse of mine, so see the comment I just posted on this for full details:

https://codereview.stackexchange.com/questions/259045/poor-m...