5 hours ago
- Regular expressions in programming are far more powerful than the formal 'regular languages' theory suggests, capable of matching context-free and even some context-sensitive languages.
- The Chomsky hierarchy categorizes formal languages, and modern regex implementations like PCRE can handle languages beyond regular ones, including those with recursive patterns.
- Using recursive subpatterns (e.g., (?1)) allows regex to match context-free languages like {a^n b^n}.
- Grammar definitions can be directly translated into regex using DEFINE and named subpatterns, as shown with an RFC 5322 email regex.