TeX is more or less one big pascal function with lots of gotos. While this makes it very hard to port to a more modular (and non-pascal) system, the source code

TeX is more or less one big pascal function with lots of gotos. While this makes it very hard to port to a more modular (and non-pascal) system, the source code (in typeset format: http://abel.math.umu.se/~lars/misc/tex.pdf http://abel.math.umu.se/~lars/misc/tex.pdf) is very readable.