A few years ago, I played with Pegged. Pegged is a PEG parser fro DLang. Beyond about why PEG is good/bad, Pegged shows how powerful is the metaprogramming of DLang. It simply generates the parser from the PEG grammar at compile time, and could execute and parse stuff at runtime and compile time ! https://tour.dlang.org/tour/en/dub/pegged