Oh, there's apparently a repl for clang/c++: "cling"

http://code-ballads.net/read-eval-print-loop-repl-in-c/

https://code-ballads.net/generated-notebooks/cpp/repl_cling/...

https://github.com/root-project/cling

https://blog.jupyter.org/interactive-workflows-for-c-with-ju...

There's been some discussion on hn before, but I couldn't find anything particularly recent (or interesting tbh).

Then there is of course rr, as seen recently on hn:

"Instant replay: Debugging C and C++ programs with rr" https://news.ycombinator.com/item?id=27034588

And I also came across "inspector"- which unfortunately appears to be abandoned?

"Inspector - A drop-anywhere C++ Repl" https://news.ycombinator.com/item?id=16360738