class Nokogiri::CSS::Parser

def [] string
  return unless @cache_on
  @mutex.synchronize { @cache[string] }
end

def []= string, value
  return value unless @cache_on
  @mutex.synchronize { @cache[string] = value }
end

def clear_cache
  @mutex.synchronize { @cache = {} }
end

def on_error error_token_id, error_value, value_stack
  after = value_stack.compact.last
  raise SyntaxError.new("unexpected '#{error_value}' after '#{after}'")
end

def parse string
  new.parse(string)
end

def without_cache &block
  tmp = @cache_on
  @cache_on = false
  block.call
  @cache_on = tmp
end

def xpath_for string, options={}
  new.xpath_for(string, options)
end

def xpath_for string, options={}
  v = self.class[string]
  return v if v
  prefix = options[:prefix] || nil
  visitor = options[:visitor] || nil
  args = [prefix, visitor]
  self.class[string] = parse(string).map { |ast|
    ast.to_xpath(prefix, visitor)
  }
end