The unravel LaTeX package provides tools to explore TeX code,
performing expansion and assignments step by step.
TeX is a strange beast. Its eyes read files, making characters into tokens. Its mouth then chews tokens, expanding them if possible, namely, expanding user-defined macros, or conditionals, etc. When meeting a so called 'unexpandable' token, TeX's stomach comes into play, performing assignments, or moving boxes around, eventually typesetting the result thanks to its great line- and page-breaking algorithms.
All of this is interleaved, and difficult to follow. Of course,
one can always use \tracingall, but the result is... messy.
This package is an attempt to replicate how TeX digests tokens,
and to make the process easier to follow. Namely,
\unravel{\some\tokens} will let you go through expansions and
assignments performed by TeX upon seeing of \some\tokens,
step by step.
Some parts of TeX are not covered. In particular, category codes
are fixed for the whole argument of \unravel when it is read.
The package is extracted by running pdflatex unravel.ins.
For the documentation, run pdflatex unravel.dtx twice.
This is work in progress, all suggestions/comments/bug reports are welcome! See https://github.com/blefloch/latex-unravel/