I've worked on production compilers for the bulk of my 40-year career. I prefer optimizers and code generators, but recently had to build a parser for modern Fortran for LLVM, and just used parser combinators to construct a recursive descent recognizer over a normalized contiguous source string in memory. The theory of formal languages is interesting but I think that the whole project of "compiler-compilers" from the 70's and 80's was working toward a solution that's inferior to where we are today with better tooling and less theory.