The odd part is that this is not just for fun. For many physicists when I was at CERN, a C++ REPL was a commonly used tool to interactively debug analyses to su

The odd part is that this is not just for fun. For many physicists when I was at CERN, a C++ REPL was a commonly used tool to interactively debug analyses to such a degree that many never compiled their code. Back then, I believe, it was some custom implementation included in ROOT (https://root.cern/ https://root.cern/). I even went out of my way to write C++ code compatible to it just so it could run in that custom C++ REPL implementation, otherwise some colleagues weren't interested in collaborating at all.