That is one of the things this update specifically addresses (and the next 1.9 will do more of). There's a tangible difference in the REPL, things feel snappier

That is one of the things this update specifically addresses (and the next 1.9 will do more of). There's a tangible difference in the REPL, things feel snappier. I'm sure there will still be lags in the odd place, and there's still a first time compilation, but that compiled result is cached a lot more, and so when you restart session as you mention below, that cache will be preserved.