Thanks for your interest in ATS3!
I am still in the midst of implementing ATS3. More precisely, I am
in the midst of implementing a type-checker for dependent types
and linear types. The required effort seems to have far exceeded
what I expected.
Up to ATS2, ATS was largely a vehicle for experimentation.
If I remember correctly, ATS0 (that is, ATS/Proto) is probably the most
feature-rich one among all editions of ATS so far; it contains many features
(e.g., OOP and typed meta-programming based on macros) that are removed
in later editions of ATS.
As I feel that ATS3 is very likely the last edition of ATS that I will ever be implementing,
I tend to think a lot more before I actually write down code. So the implementation
does take a lot longer this time. The good news is that I should be able to move a bit
faster once I finish this type-checker, which undoubtedly is the most challenging part
of implementing ATS3. Very optimistically, I expect to see some version of ATS3 that is
able to compile to C/C++. Keep tuned :)