Also no (official) REPL.

Actually Java has had a repl called Jshell since JDK 9.

The Julia crowd really need to hang less value on the REPL - people writing serious production code don't use one, and scientists using Python have moved on to notebooks. At this point, having Julia be so focused on the REPL is a weird affectation.

Julia has great notebook support, the Ju in Jupyter stands for Julia after all. There's also the fantastic Pluto.jl for reactive notebooks.

And the VSCode extension isn't quite IDE level, but that's just a matter of resources.

I'm a scientist, I use REPL a ton. Notebooks are fine too, but there's a thing called exploration and nothing beats REPL speed for that.

In future it would be great to mashup something like repl.it with Jupyter notebooks, maybe with Medium-style wysiwyg. That might really win.

I used notebooks when I did my PhD using Python, but have moved to the REPL using Julia on my PostDoc. The Julia REPL experience is so much nicer than Python's, it removes the need for notebooks completely for me.

IMO, the REPL is really nice for exploration. I would never write code in it, but it serves as a really good doc search tool and quick way to check things. It helps that the Julia REPL is more inspired by the Lispy ones than python/R.

Mediocre performance compared to what?