This is fascinating. I could see it being very useful for writing SIMD abstraction layers (like Highway or SIMDe) without so much of the cruft.

> For example, instead of a power function that uses a loop, you could generate specialized code like x * x * x * x * x directly. This eliminates runtime overhead and creates highly optimized code.

Could anyone explain to me how this is different from templates or parameter pack expansion in C++? I can see the constexpr-ness here is encoded in the type system and appears more composable, but I am not sure if I am missing the point.

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

How is this different from a syntactic macro?

  - it is typed, and

  - multi-stage programming can also describe runtime-code generation.