I feel the pain of a lack of REPL. I frequently want to check a snippet of code, but need to go through the cycle of creating a test case, copying code, modifying it so that it works standalone without its context, running it and then deleting it. It's tiresome.

As for compilation, yes, it's slow in general, but once you compile a project initially, later incremental builds are usually quick.

Overall, I think in the future I'll see if I can use SML more and see how it goes.