Incidentally I spent yesterday implementing a Lisp formatter with the algorithm described by Jean-Philippe Bernardy in the simple and elegant paper "A Pretty But Not Greedy Printer."

https://jyp.github.io/pdf/Prettiest.pdf

It's based on introducing choice between vertical and horizontal stacking. It avoids combinatorial explosion by pruning away strictly suboptimal choices. With just a few extra rules for Lisp forms, the results are quite good.

I don't handle comments though, since I only need it for pretty printing values so far.

I also wrote a version of Bernardy's pretty printer, but I never did come up with a satisfactory way of formatting text together with code. The best looking solution of splitting on whitespace and making each word a group, either tacking it onto the current line or splitting onto a new line ends up being exponential even with pretty aggressive optimization. Everything else I tried looked bad.