Is there a regular expression to detect a valid regular expression? (2008)(stackoverflow.com)
stackoverflow.com
Is there a regular expression to detect a valid regular expression? (2008)
https://stackoverflow.com/questions/172303/is-there-a-regular-expression-to-detect-a-valid-regular-expression
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"regualr stuff" : https://www.geeksforgeeks.org/regular-expressions-regular-gr...
Related:
Is there a regular expression to detect a valid regular expression? - https://news.ycombinator.com/item?id=20909939 - Sept 2019 (219 comments)
Is there a regular expression to detect a valid regular expression? - https://news.ycombinator.com/item?id=20909939 - Sept 2019 (219 comments)
Other than the appealing symmetry of being able to use a language to parse that same language, this feels very similar to https://stackoverflow.com/questions/1732348/regex-match-open...
Edit: I just checked and sadly someone beat me to it in 2019: https://news.ycombinator.com/item?id=20910120
Edit: I just checked and sadly someone beat me to it in 2019: https://news.ycombinator.com/item?id=20910120
Damian Conway's https://metacpan.org/pod/PPR module defines a regex (in the commonly used sense) that can match perl source code - including perl regexes!
Edit: "The PPR module provides a single regular expression that defines a set of independent subpatterns suitable for matching entire Perl documents, as well as a wide range of individual syntactic components of Perl (i.e. statements, expressions, control blocks, variables, etc.)"
Edit: "The PPR module provides a single regular expression that defines a set of independent subpatterns suitable for matching entire Perl documents, as well as a wide range of individual syntactic components of Perl (i.e. statements, expressions, control blocks, variables, etc.)"
I answered a funny regex question once, “can strings that are base64 encoded twice be matched with a regex?”
https://stackoverflow.com/questions/49650847/determine-if-st...
The answer is yes, they’re regular. :-D
https://stackoverflow.com/questions/49650847/determine-if-st...
The answer is yes, they’re regular. :-D
That's amazing. Thank you!
The user ID that asked the question looks to have last answered a question in 2016.
I'm not sure what this means. Have we asked and answered all the good questions already?
I'm not sure what this means. Have we asked and answered all the good questions already?
Technically, the set of strings containing balanced parentheses is not a regular language...
Oh man you've already got two problems? Maybe it's four now.
What about a regular expression that detects regular expressions that detect valid regular expressions?
protip: a language is not regular if you need counter(s) to parse it.
protip 2: good regex implementations often have extensions that support counters.
protip 2: good regex implementations often have extensions that support counters.
[0] : https://web.mit.edu/6.005/www/fa15/classes/17-regex-grammars...
[1] : https://peerj.com/preprints/1248.pdf
[2] : https://www.cs.ox.ac.uk/ralf.hinze/WG2.8/28/slides/fritz-pap...
[3] : https://www.npmjs.com/package/regexp-tree
[4] : example bnf grammar for regular expressions : https://github.com/DmitrySoshnikov/regexp-tree/blob/master/s...