It looks good to me. I'm a big fan of RPN and old HP calculators. Next step: implement a "False" interpreter. <https://esolangs.org/wiki/FALSE>
Advanced step after that: read up on the "Joy" language by Manfred von Thun, and implement your own version. <https://web.archive.org/web/20101112212930/http://www.latrobe.edu.au/philosophy/phimvt/joy.html> My own language, Listack, has v0.3 written in Nim. You can use that as an example or starting point. No, it's not terribly efficient, and probably isn't particularly well written. Yes, I keep meaning to write a new, better version.
