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Just out of curiosity, is it possible to parse a string that is totally made out of random but valid regular expressions with a single regular expression?
given the string of regex:
<[^>]*>\xA9
parses to:
<[^>]*>
\xA9
in which the first one match html and second one match a copyright symbol.
Edit:
I found a similar question asked at SO claiming that it maybe possible. Here, I’m referring to regex in JavaScript ECMA-262 only.
No, it is not possible: regular expression language allows parenthesized expressions representing capturing and non-capturing groups, lookarounds, etc., where parentheses must be balanced. It is not possible even in theory to write a regular expression that verifies if parentheses are balanced in a given string. Without an ability to do that you wouldn’t know where one regexp ends and the other one starts.
In general, regex grammar is relatively complex. To get an idea of just how complex it is, take a look at the parser in the source of Java’s
Patternclass.