Is ConTeXt using TeX or rewriting it?

Question

Just out of curiosity, is ConTeXt using the TeX algorithm in it's entirety, or are some components rewritten?

If it's the latter:

1. Could all of TeX be rewritten in Lua, or are there good reasons against it?
2. How was the pascal translated to Lua - automatically, or did someone understand it in it's entirety and rewrite it?

Feel free to close this as off-topic

Answer 1

ConTeXt is mainly a macro package written in the TeX language. The current version MkIV is written for the TeX backend LuaTeX, which is written in C and opens up part of the TeX internals to a Lua interpreter, which the ConTeXt macros heavily use.

Could all of TeX be rewritten in Lua, or are there good reasons against it?

Sure, nothing prevents you from rewriting TeX in Lua, but it would not make much sense. It already has a brilliant C implementation with Lua interface. What would be the benefit?

How was the pascal translated to Lua - automatically, or did someone understand it in it's entirety and rewrite it?

The pascal code was never translated to Lua. The pascal code has been manually converted to C.

Here are some slides which depict how LuaTeX is comprised: Taco-LuaTeX-talk-2007

Answer 2

The Luatex project, as outlined by Taco in the link Marco gave, isn't about reimplementing Tex, it's about:

1. Exposing Pdftex's internal data structures to Lua;
2. Adding hooks into the Pdftex engine, e.g., callbacks; and
3. Using Lua as a bridge to other code, most importantly Metapost, through mplib.

This allows Lua to be involved in layout, but the that is through configuration, scheduling and controlling the Pdftex engine which does the real work.

Context uses Lua to make scripting easier, and because it can potentially make heavy use of Metapost in layout. But the heart is basically Knuth's algorithms. Note also that Context Mk II did not use Lua, so much of Mk IV's functionality does not depend on what is new with Luatex.