module Regexp::Parser

def self.parse(input, syntax = "ruby/#{RUBY_VERSION}", &block)
  @nesting = [@root = @node = Root.new]
  @conditional_nesting = []
  Regexp::Lexer.scan(input, syntax) do |token|
    parse_token token
  end
  if block_given?
    block.call @root
  else
    @root
  end
end