> Furthermore, the effort to rewrite as much of the TeX implementation as possible in Lua is perplexing. Very little of the TeX implementation has been rewritt

> Furthermore, the effort to rewrite as much of the TeX implementation as possible in Lua is perplexing. Very little of the TeX implementation has been rewritten in Lua. (Assuming you're talking of LuaTeX itself and not the "TeX without TeX" wiki page, which is just for demonstration.) LuaTeX starts with the WEB (Pascal) code of TeX, manually translated into C (see e.g. https://tug.org/TUGboat/tb30-3/tb96hoekwater-pascal.pdf https://tug.org/TUGboat/tb30-3/tb96hoekwater-pascal.pdf), and, additionally, hooks are added: callbacks that can be written in Lua, and which have access to the internal data structures. (By the way, SILE is a separate typesetting system (unrelated to TeX) that is actually written in Lua, and re-implements some of the TeX algorithms in Lua, I think. You can see this talk by its author about it: https://www.youtube.com/watch?v=5BIP_N9qQm4 https://www.youtube.com/watch?v=5BIP_N9qQm4 )