Seven years after his 1979 book "TEX and METAFONT", at the start of a revolution leading to ubiquitous desktop publishing (first Macintosh in 1984), Knuth published a set of five books on TEX, METAFONT, and typefaces.
His purpose as teacher was to show a new way to write and document computer programs -- "literate" programming. In these volumes Knuth published two sizeable PASCAL applications for computerized typesetting and -- as a byproduct -- invented a documentation tool, CWEB, that both preserves the textual accuracy of the source code and improves programmer comprehension for debugging and maintenance purposes.
The peer review process implied by Knuth's demonstration, his careful attention to the tiniest details, and his gift of the source code to the public domain are all foundations of today's open source community.
This is hardly an introductory text on programming and very few of us read computer programs for fun. That said, a programmer with some experience could learn a great deal by thorough study and imitation of the master craftsmen (don't forget about John D. Hobby) at work here.