It's a bit old, of course, but TeX: The Program is still a fascinating read because of the exceptional attention that Knuth has paid to exposition, especially f

It's a bit old, of course, but TeX: The Program is still a fascinating read because of the exceptional attention that Knuth has paid to exposition, especially for a program that size. Besides, TeX is still being used after almost 40 years, so it's inarguable that Knuth did some things right. https://www.amazon.com/Computers-Typesetting-B-TeX-Program/dp/0201134373/ref=sr_1_1?ie=UTF8&qid=1482267413&sr=8-1&keywords=tex+the+program https://www.amazon.com/Computers-Typesetting-B-TeX-Program/d...