Recursive Patterns

• With the (?1) notation things are a little easier.

• • if ('(x(x)y(x)x)'=~m/^(\((?>[^()]++|(?1))*\))$/x)
  • { ... }

• Advantages:

• • Faster – Perl interpreter is not involved. Since pattern may not change the engine can optimize the pattern.
  • Smaller – pattern need not be duplicated
  • Self contained –no global vars
  • Self describing – pattern is self contained. Context is not required to see what the pattern matches.