Going by OP's description, Flex and Bison appear to be well suited for what he/she intends to do. There is a bit of a learning curve, but I think it's well worth it. I have been working with both for a few years now and find them very flexible.

FYI, Bison supports parsers using either LALR(1) (Look-Ahead Left-to-Right with 1 token lookahead) [https://en.wikipedia.org/wiki/LALR_parser] or GLR (generalized Left-To-Right) [https://en.wikipedia.org/wiki/GLR_parser].

O'Reilly's book "flex & bison" by John Levine is a helpful reference. [https://www.amazon.com/flex-bison-Text-Processing-Tools/dp/0...]