[democat]

You are absolutely spot on. Both systems are Turing-complete, so a perfect conversion without a full runtime execution is theoretically impossible for the general case. That's exactly the trade-off Tylax makes: we aren't trying to be a full TeX engine (which would be overkill and slow). Instead, we aim to cover the "99% use case" of academic and technical writing—where macros are mostly used for shorthand, notation aliases, or simple formatting, rather than complex computation. Our "limited macro expander" is the middle ground: it's dumb enough to be fast and safe (no infinite loops), but smart enough to handle the \newcommand shortcuts that riddle almost every paper. It's about being pragmatically useful rather than theoretically perfect