The cookbook[0] has some good examples, I went with the state machine parser
as a base for highlighting in mpv's console (mpv scripting has been the main focus of my fennel use, mostly rewriting existing code)
Thanks, Life w/TIC-80 seems like a good candidate. Simple enough that I can wrap my head around the whole thing and tweak the rules, even though it's (to me) an alien syntax and structure.
[0] https://github.com/bakpakin/Fennel/wiki/Cookbook