Hashtable/dictionary/map lookup with regular expressions

Question

I\'m trying to figure out if there\'s a reasonably efficient way to perform a lookup in a dictionary (or a hash, or a map, or whatever your favorite language calls it) where the

Answer 1

What you want to do is very similar to what is supported by xrdb. They only support a fairly minimal notion of globbing however.

Internally you can implement a larger family of regular languages than theirs by storing your regular expressions as a character trie.

• single characters just become trie nodes.
• .'s become wildcard insertions covering all children of the current trie node.
• *'s become back links in the trie to node at the start of the previous item.
• [a-z] ranges insert the same subsequent child nodes repeatedly under each of the characters in the range. With care, while inserts/updates may be somewhat expensive the search can be linear in the size of the string. With some placeholder stuff the common combinatorial explosion cases can be kept under control.
• (foo)|(bar) nodes become multiple insertions

This doesn't handle regexes that occur at arbitrary points in the string, but that can be modeled by wrapping your regex with .* on either side.

Perl has a couple of Text::Trie -like modules you can raid for ideas. (Heck I think I even wrote one of them way back when)