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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, f

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.

simonebrunozzi 6y ago
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.
andialo 6y ago
That's really impressive work. What flavor of regular expressions do you follow there?
- robertelder 6y ago
  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-grammar/ 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.
  - indentit 6y ago
    Any chance of open sourcing it so we can contribute some regex features to your awesome project? :)
chii 6y ago
I tried using this expression: ^((?:(?:https?|ftps?):\/\/)|irc:\/\/|mailto:)([\w?!~^\/\\#$%&'()*+,\-.\/:;<=@]*[\w~^\/\\#$%&'()*+,\-\/:;<=@]) and it seems to fail to visualize it.
- robertelder 6y ago
  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_regex=%5E(((https%3F%7Cftps%3F)%3A%5C%2F%5C%2F)%7Circ%3A%5C%2F%5C%2F%7Cmailto%3A)(%5B%5Cw%3F!~%5E%5C%2F%5C%5C%23%24%25%26'()*%2B%2C%5C-.%5C%2F%3A%3B%3C%3D%40%5D*%5B%5Cw~%5E%5C%2F%5C%5C%23%24%25%26'()*%2B%2C%5C-%5C%2F%3A%3B%3C%3D%40%5D)&the_subject=mailto%3A%5Ep81 https://blog.robertelder.org/regular-expression-visualizer/?...
  - Serow225 6y ago
    The first one that I tried also failed for the same reason, FWIW. Cool tool! :)
mlyle 6y ago
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.
- robertelder 6y ago
  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.
  - mlyle 6y ago
    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...

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.

simonebrunozzi 6y ago

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.

andialo 6y ago

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

robertelder 6y ago
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-grammar/ 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.
- indentit 6y ago
  Any chance of open sourcing it so we can contribute some regex features to your awesome project? :)

chii 6y ago

I tried using this expression: ^((?:(?:https?|ftps?):\/\/)|irc:\/\/|mailto:)([\w?!~^\/\\#$%&'()*+,\-.\/:;<=@]*[\w~^\/\\#$%&'()*+,\-\/:;<=@]) and it seems to fail to visualize it.

robertelder 6y ago
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_regex=%5E(((https%3F%7Cftps%3F)%3A%5C%2F%5C%2F)%7Circ%3A%5C%2F%5C%2F%7Cmailto%3A)(%5B%5Cw%3F!~%5E%5C%2F%5C%5C%23%24%25%26'()*%2B%2C%5C-.%5C%2F%3A%3B%3C%3D%40%5D*%5B%5Cw~%5E%5C%2F%5C%5C%23%24%25%26'()*%2B%2C%5C-%5C%2F%3A%3B%3C%3D%40%5D)&the_subject=mailto%3A%5Ep81 https://blog.robertelder.org/regular-expression-visualizer/?...
- Serow225 6y ago
  The first one that I tried also failed for the same reason, FWIW. Cool tool! :)

mlyle 6y ago

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.

robertelder 6y ago
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.
- mlyle 6y ago
  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...