miniblog.

What software designs require clean slate 'revolution' implementations, rather than evolution? I can think of: borrow checking in a PL (existing code is unsafe), microkernels (architecture is too different from monokernels), and full REPLs (can't add type redefinition later).

One interesting property of both stdin/stdout based REPLs and RPC based REPLs is that they need to support asynchronous events. In both these programs, I don't need to wait until the function is done to see the output printed. It's not sufficient to read-eval-wait-print-loop.

There's something of a tradition of REPLs having personalities in lisp. I've seen Common Lisp tools (e.g. slime/sly) and Clojure (e.g. cider) say encouraging things, but Fennel is almost judgemental :)