Recursive Patterns Using Eval

• Old way – dynamic patterns

• • our $pat;
  • $pat = qr/\((?>(?>[^()]+)|(??{$pat}))*\)/x;
  • if ('(x(x)y(x)x)' =~ /^($pat)$/){ ... }

• Inherent problems

• • Slow – requires the interpreter to resolve what $pat holds
  • Fat – requires two patterns (inner and outer)
  • Clumsy – requires use of global vars
  • Ugly – pattern is not self contained. Pattern does not in of itself explain what it does.