RegexpHash: Hash subclass for building nested regular expressions

regexp_hash.rb

class RegexpHash < Hash
  def add_word(word, hsh = nil)
    hsh ||= self

    return unless (word && word.length > 0)
    key = word.slice(0..0)
    hsh[key] ||= {}
    add_word(word.slice(1..-1), hsh[key])    
  end

  def flatten!(hsh = nil)
    hsh ||= self
    hsh.keys.each do |key|
      if hsh[key] && (hsh[key].keys.length == 1)
        child_key = hsh[key].keys[0]
        child_value = hsh[key][child_key]
        hsh[key + child_key] = child_value
        hsh.delete(key)
        flatten!(hsh) if child_value
      else
        flatten!(hsh[key]) if hsh[key]
      end
    end
  end

  def to_regexp
    flatten!
    pattern = self.inspect.
      gsub("{", "(").
      gsub("}", ")").
      gsub(',', '|').
      gsub('()', '').
      gsub(/(\"|=\>|\s)/,'')
    Regexp.new(pattern)
  end
end

store = RegexpHash.new

["doggy", "dolly", "dilbert", "dogbert"].each do |word|
  store.add_word(word)
end

puts store.to_regexp
# => (?-mix:(d(o(lly|g(bert|gy))|ilbert)))

p "doggy dolly bert xxxdogbertxxx".scan(store.to_regexp)
# => [["doggy", "oggy", "ggy", "gy"], ["dolly", "olly", "lly", nil], ["dogbert", "ogbert", "gbert", "bert"]]