I'm not the author, but my impression is that he wanted a single compiler that both compiles fast and generates fast code. I think it's a good goal, although i

I'm not the author, but my impression is that he wanted a single compiler that both compiles fast and generates fast code. I think it's a good goal, although if you take into account total engineering effort, my suspicion is that having a separate interpreter and a compiler is an accepted (if not common) solution for that reason. I think you're saying you don't need to compile fast to be interactive, because you can just use a slow compiler on tiny snippets of code, and patch them in. That seems like a fair point. (Python doesn't count, because it doesn't run fast, but Swift probably does. As far as I know the Swift playgrounds use the compiler at runtime. Java doesn't fit the requirements based on "predictable, explainable performance". You can of course quibble with that requirement) I do wish every language had a REPL and a compiler. And the interaction with language design is definitely worth exploring. I think Java and Swift have the tech, but I never really hear about people using them interactively, maybe because the languages themselves aren't great for typing in. (as opposed to R or shell or Lisp; Python could do better here too)