[owl57]

Data point. I just converted a small app to Elm 0.19. So, that's a real 0.x: breaking API changes all across the standard library. I just repeatedly ran the compiler and jumped to the next error. About an hour for my 1 KLOC app (and Elm code is pretty sparse), seems rather tedious. But! Now it works again, and I believe it to be working just as good as before. Of course there could be some new bugs, but I would rather expect them in the substantially changed parts of the Elm runtime than in my app where I didn't look at anything compiler didn't tell me to look at.

I have even less experience with OCaml, but my gut feeling is that it should be about the same in this respect unless you let mutable state run wild.