I can't imagine a language even starting to displace Python without a good REPL. Not just a hacked-together "lol does this work" REPL, something you can rely on

I can't imagine a language even starting to displace Python without a good REPL. Not just a hacked-together "lol does this work" REPL, something you can rely on, and preferably something you can use as a Jupyter backend.