I don't know if JVM is a problem; the issue that caught me in my few-weeks of experimenting with the language was the lazy semantics of sequences.

I know the problem, and I've danced around this same issue in things like Haskell with strictness annotations, and I've run into the same problem in R, but I'd like to just be able to read and parse a ~1GB CSV file without blowing out RAM with a giant list of thunks.

This was many years ago now, so maybe they've fixed it, but I'm tired of fighting that particular battle.