Oh, wow! This looks great! I generally like the GPL (including 3) - but wonder if MIT/BSD moght not have been an even better choice for a text book, where someone might want to build on example code and use it in a different system.
At any rate the PDF version looks (and more importantly reads) great.
I volunteered at the Free Software Foundation for about 2 years when I was a student at MIT.
GPL is almost always a bad choice for open source projects. I could write for days on the subject - but I'll try to be brief.
(Note: I am not a lawyer and not speaking on behalf of the FSF, just on my own capacity.)
This was during the years Linux was the rebel, Microsoft was the suits, and you could plop the GPL on anything and people would embrace it as the worlds. Code was open - but untouchable by the corporations.
To my surprise, after joining them rank and file of the private sector people chided me for my enthusiasm in the GPL.
I realize in retrospect the youthful folly of it. It turns out the "poison pill" that is the derivative work clause of the license affects everybody. That is, hardware vendors, game makers, medium sized companies, small companies, individuals, even more permissively licensed open source projects can't touch GPL.
What took me years to realize is when corporate brought us into a meeting with the lawyers, LGPL and GPL w/ exceptions are in the same boat! These exceptions are weak compared to the 9 pages of restrictions biased toward the virility of it.
What made me really popular in open source, made me an outcast at work. It got me, fresh out of MIT, fired, and for a time on welfare (only for the period of 2 weeks).
GPL uses the term "Free" in a twisted, marxist way. It's restrictive and, while done in good faith, completely burns bridges and appeal to people who'd otherwise be happy contributing upstream to some projects.
Reminder, I am not a lawyer and was only a volunteer at FSF. I still accept GPL for some projects, but my opinion has since changed since entering the workforce.
Looking at the code on GitHub[1] I don't understand how this qualifies as "literate" programming. I'm also not quite sure why you'd version binaries as well as /etc/passwd... There's also an awful lot of "// old line comment removed". Maybe I'm confused but this does not "read like a book".
EDIT: I found what I was looking for [2].
[1]: https://github.com/hgesser/ulix
[2]: https://raw.githubusercontent.com/hgesser/ulix/master/ulix-b...