Haha, funny. I also wrote something similar for working with KiCad files, naming it Sexprs, also in Rust. I was worried someone had found it and posted it here.

Is there a way to modify and re-emit them at runtime? Seems neat, but the readme is lacking.

The code in the screenshot/asciinema isn't s-expr by any common conception of the term, or as a Lisp would parse it.

  (flatten '( '(a '( b)) '( c   d)))

That argument to flatten is in fact [macroexpanding manually, forgive errors]

  '((quote (a (quote (b)))) (quote c d))

which flattens to

  '(quote a quote b quote c d)

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Parsing sexprs is quite easy, no need to use a complex parser generator. The core of parsing sexprs is you have a "read_list" function, which accumulates values until it finds a ')', and whenever you encounter a '(' character, you recurse into that same read_list function. You don't even need a lexer.

Also, this is divided in 8 crates for some reason... don't take this the wrong way, but is it the result of vibe coding?