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Comment by robertelder | Hacker News Reader

Hi, I'm the author of this page. This tool has a lot of complexity in it and a huge number of corner-cases. If you discover any bugs or XSS vulnerabilities, feel free to let me know.

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This is fantastic, thanks for sharing it.

I wish I had it when I was a CS professor in 2004-2006, teaching Compilers to 2nd year university students. They would have found it really useful.

I'm having trouble with backtracking and groups. It's possible I'm doing something wrong, but

    [bc]*(cd)+

doesn't seem to match

cbcdcd

Nor does the simpler

    a*(ab)

match

aab

But

    a*ab

matches aab.

You found a bug. The bug was: When I was computing the animation frames for the visual, after a backtracking event, I forgot to restore the 'progress' values for the PROGRESS nodes to what they were before the stack push took place. I think I fixed this issue, and I just pushed an update which should appear any second when the cache invalidates.

Cool! Thanks for looking at it/fixing it.

P.S. The whole split() thing you do is an interesting hack to not have to preserve/rewind so much state. :D I've never quite seen fork() used so...

I tried using this expression:

   ^((?:(?:https?|ftps?):\/\/)|irc:\/\/|mailto:)([\w?!~^\/\\#$%&'()*+,\-.\/:;<=@]*[\w~^\/\\#$%&'()*+,\-\/:;<=@])

and it seems to fail to visualize it.

The (?:stuff) part is for a non-capturing group which I didn't add support for. Maybe in the near future. That would be one of the easiest features to add since the tool also doesn't support backreferences yet.

Edit: Actually, since the non-capturing group part doesn't add much here, you can just remove the '?:'s and this works:

https://blog.robertelder.org/regular-expression-visualizer/?...

The first one that I tried also failed for the same reason, FWIW. Cool tool! :)

That's really impressive work. What flavor of regular expressions do you follow there?

I tried to follow a middle-of-the-road works mostly everywhere made up flavour. Here is a grammar for it:

https://blog.robertelder.org/regular-expression-parser-gramm...

I may add to it in the future if there is enough interest. At the moment it doesn't support a few common things like word breaks and backreferences, but I don't think it'd be too hard to add.

Any chance of open sourcing it so we can contribute some regex features to your awesome project? :)

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