class Geocoder::Lookup::Maxmind

def configured_service!
  if s = configuration[:service] and services.keys.include?(s)
    return s
  else
    raise(
      Geocoder::ConfigurationError,
      "When using MaxMind you MUST specify a service name: " +
      "Geocoder.configure(:maxmind => {:service => ...}), " +
      "where '...' is one of: #{services.keys.inspect}"
    )
  end
end