Comment by breck

I absolutely love parser combinators, and years ago I did a huge rewrite of my compiler compiler so that it'd have the easiest possible parser combinators: simple string concatenation. grammarA + grammarB = grammarC. You can play with that here (https://jtree.treenotation.org/designer/). You still need to make a line change or two (good design after all, requires some integration), but it just works. Haven't seen anything beat it and not sure if that's possible. (Note: I do apologize for the crappy UX, and it's high on the priority list to give the app a refresh)