Thank you very much for your review. I didn't know about https://news.pub/. It's a great place!

By default, expr's make compiles tests and examples. Among them is calc, a basic little tool that allows you to test expressions.

Nice contribution! Seems that you are using Lezer for handling the parsing. Multi-type parsers are a fascinating subject but I haven’t encountered many references to them either. It would be interesting to explore more projects or approaches in that area. Contributions are welcome!

Yes, I used the 'yy_' prefix to indicate that they are parsing-related functions, and also as a tribute to Yacc/Bison. You're not the first person who finds this creepy. Maybe I should change the prefix...