Let me tell you why you should (nearly) never use PEG (parsing expression grammars). Nearly everything I will say applies to parser combinators (parsec in Haskell, nom in Rust), too. So, don't use PEG. Use CFGs (context-free grammars) instead. They are more natural. I feel that CFGs more naturally represent how we think. Thus when you have some language in your head and you try to write it down as
