I'm aware of derivatives. My concern with derivatives (which I think are awesome) is that the combinatorial blow-up that we associate with DFAs is always around

I'm aware of derivatives. My concern with derivatives (which I think are awesome) is that the combinatorial blow-up that we associate with DFAs is always around the corner. I've never been a huge fan of putting all my eggs in the the 'I hope it won't explode' basket. It's been a major point of difference with RE2 all this time - IMO you need a high performance pass for things that don't determinize cleanly (even when you are doing lazy determinization). I would need to see a lot more detail on using derivatives for capturing groups and back-references. Sorry if I sound closed-minded, but derivatives look like they solve a lot of stuff I already know how to do really well.