This is a really nice and illuminating post!

Especially cool how all evaluation is done by line 33. (Minor comment: Line 14 may benefit from using a different variable for the function instead of “c”.)

An “aside” comment, as the title mentions “literate C++” [Edit: This was submitted as something like “Build me a Lisp: in less than 50 lines of literate C++”]. This post exemplifies one aspect of literate programming (as Knuth envisioned it), which is “let us concentrate rather on explaining to human beings what we want a computer to do.”

But there are two further features that Knuth-style LP systems have, which are missing here:

• The ability to write your program / explanation in any order (ideally, an order that is best for presentation, rather than an order demanded by the compiler). In this case, the program is explained strictly in the order of lines in the program, which imposes some awkwardness. (Not only in the explanation, but also in the code: e.g. putting a #include on line 34 of 49.)

• Named chunks. So instead of writing

    int main() {
        try {

in one code block, and having to continue it later, you could write something like, say,

    int main() {
        try {
            [[say hello world]]
        } [[handle errors]]

and later fill in the corresponding sections by name.

The original examples by Knuth are somewhat hard to read because they were written in Pascal and the programs were quite low-level but there's a great example available today (a book which won an Academy Award!), now free online — http://www.pbr-book.org/ (random page: http://www.pbr-book.org/3ed-2018/Light_Transport_I_Surface_R... )

But then again, the “no-tools” approach here does have the advantage of not requiring any special build step and not requiring the reader to understand any such conventions, so I guess that's a tradeoff. (They say one of the reasons literate programming never took off is that there are as many literate-programming tools as the number of people trying literate programming; everyone ends up having to write the tool that works for them.)