I'm attempting to use Control.Event to limit HTTP requests made by a dippy little scraper I'm constructing to once per second but I think, maybe, that the Events are not being evaluated. First, some imports.
import qualified Data.ByteString as B import qualified Data.ByteString.Char8 as C import Network.Curl.Download import Network.Curl.Opts import System.Exit import System.Environment import System.Time import Control.Event import Control.Monad import Data.Char
The Event function of this program is append. It takes a local path and a URL, retrieves the contents pointed to by the URL and appends them to the local path. The function download, below, performs the retrieval.
append :: FilePath -> C.ByteString -> IO () append f u = B.appendFile f . addNew . C.filter (not . isAscii) =<< download u where addNew = C.append (C.pack "\n")
download :: B.ByteString -> IO B.ByteString download url = do res <- openURIWithOpts [CurlEncoding "gzip", CurlUserAgent "aule-0.0.2"] $ C.unpack url case res of Left _ -> exitFailure Right cont -> B.putStrLn cont >> return cont
The function sched adds a list of Events to the evtSys system, a fixed time delay between each.
sched :: EventSystem -> ClockTime -> Integer -> Integer -> (t -> IO ()) -> [t] -> IO () sched _ _ _ _ _ [] = return () sched evtSys (TOD sec _) delay mul action (x:xs) = do addEvent evtSys (TOD (sec + (delay*mul)) 0) (action x) sched evtSys (TOD sec 0) delay (mul + 1) action xs
main is, as usual, pretty boring. The program compiles and runs, but no output file is made. This being one of my first appreciable Haskell programs, I rather imagine I've run into a strictness problem, maybe. Would someone be so kind as to steer me in the right direction?
main :: IO () main = do [i, o] <- getArgs eS <- initEventSystem t <- getClockTime inp <- B.readFile i sched eS t 1 1 (append o) (C.lines inp)
Thanks, Brian