Those aren’t necessarily written as people would do it today, but Knuth’s literate sources for TeX[1] and METAFONT[2] are explicitly meant for reading. The lite

Those aren’t necessarily written as people would do it today, but Knuth’s literate sources for TeX[1] and METAFONT[2] are explicitly meant for reading. The literate program family also includes LCC[3], but A retargetable C compiler is a book that you’d need to buy; and PBRT[4], but Physically based rendering is more exposition than program (even if the program is a perfectly good one). The source for Unix V6[5] with the accompanying commentary by Lions is probably as much of a classic as it’s possible to get. And as an eccentric choice in a similar format, may I suggest cmForth[6], perhaps paired with Footsteps in an empty valley[7]? Also, though this is not precisely what you’re asking for, The architecture of open-source applications and its sequels[8] have the original designers’ reflections on some well-known codebases. [1] http://mirrors.ctan.org/info/knuth-pdf/tex/tex.pdf http://mirrors.ctan.org/info/knuth-pdf/tex/tex.pdf [2] http://mirrors.ctan.org/info/knuth-pdf/mf/mf.pdf http://mirrors.ctan.org/info/knuth-pdf/mf/mf.pdf [3] https://github.com/drh/lcc https://github.com/drh/lcc [4] https://pbr-book.org/ https://pbr-book.org/ [5] http://v6.cuzuco.com/ http://v6.cuzuco.com/ [6] https://github.com/ForthHub/cmFORTH/blob/combined/cmforth.fth https://github.com/ForthHub/cmFORTH/blob/combined/cmforth.ft... [7] http://forth.org/OffeteStore/4001-footstepsFinal.pdf http://forth.org/OffeteStore/4001-footstepsFinal.pdf [8] https://aosabook.org/ https://aosabook.org/