The relevant perldelta briefly touches on the subject of the Trie optimization for regexes. Basically, I think, the idea is that you convert the constant part of the regex into hashes of hashes that you can then walk very quickly (if you are using C instead of Perl), like the following hash to match the numbers (11,122,233,31) (except that the following is not valid Perl syntax as the hash needs to be created step-by-step to make the internal forward references work):

my %trie;
%trie = (
  1 => { 1 => 'accept', 
         2 => {
                2 => 'accept',
                3 => \%trie{2}->{3}, # since we already saw a 23
                _default => \%trie,
         }
         _default => \%trie },
  2 => { 3 => { 
                3 => 'accept',
                _default => \%trie{3}, # we already saw a 3
              },
         _default => \%trie
       },
  3 => { 1 => 'accept', _default => \%trie },
  _default => \%trie;
);

# hash walker omitted

[download]

The next step will likely be Aho-Corasick optimizations for regexes, which you can watch animated here.

Updated: After a discussion with bart, I expanded the example to shed more light on the importance of links within the %trie structure. If a match fails for 122, we can continue trying to match 223 and store the knowledge that we've already looked at 22 in the deep link within %trie.

In reply to Re^5: Regexp for range of numbers by Corion
in thread Regexp for range of numbers by loris

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