Well, write-compile loop depends on language and what you do. Of course it would be horrible experience to e.g. hack some mostly undocumented record format in Lisp REPL into ad-hoc parser routine on the screen with 1Hz refresh rate. But we may find some activities almost opposite to that example. Like, write a code (in literate programming style preferably) of some sophisticated algorithm, well-thought before, especially in language that doesn't support REPL-style well - e.g. C, where you know the tests wouldn't help you much and accuracy (and focus) is a king. And we don't have a need to strictly oppose those both activities to each other actually. Playing with REPL at home, done this part of work ('the quick part'), then take an eInk and go out to the park to slow down and think about that part ('the slow and focused part') - that sounds good for me.

The 'universal conversation app' is would be great to have on its own merit.