A crawler is a wrapped structure consisting of a start-point for the task, a front-end handler and a back-end handler. The start point is first fed to the front-end handler, which produces the results and generates to tasks to the queue. The back-end handler consumes the results passed by the front-end handler and saves them permanently.

data Crawler a b = Crawler{
    entryPoint::a,
    webHandler::OCTableT a IO b,
    dataHandler::b->IO ()
}

runCrawler::Crawler a b->IO ()

Data.OCTable