I agree that ATS isn't as user friendly or polished as Rust, but the main reason for that is ATS development is pretty much a one person development team. Hongwei works on the compiler, writes the documentation, the libraries, etc. It hasn't gained a large community yet. Rust has the advantage of a major company backing it, paying developers, writers, etc. Hopefully ATS can build a community and improve on these things.
It isn't just that ATS is understaffed. I gave up trying to contribute because I got tired of getting active pushback on basic style issues that I would expect CS undergrads to have figured out by the end of their first semester.
Seriously, "When the dust settles, we will think of better names ..."
Hongwei is a great researcher, but he hasn't displayed particularly good judgment wrt. software engineering, and no amount of external contributors can fix problems that come down to a maintainer who actively pushes bad practices. It was almost heartbreaking to walk away from ATS for me, but I came to the conclusion that I just wasn't going to be able to fix the things that needed fixing while Hongwei was making decisions like these.
At (IIRC) Hac Boston 2012, Edwin Brady gave a talk on what was at the time a very work-in-progress version of Idris. There were several points during the talk where he went to demo some basic feature in the repl, got some nasty error message, and went "oh right, I haven't implemented that yet." But even then, it felt more polished than ATS does now.
This is the exact reason I ended up picking Rust over ATS, good documentation that's getting better, and all the advantages of a huge network effect: more, better libraries, community you can ask for help, books, more research, etc...
