On Tue, Nov 29, 2005 at 12:00:03PM -0000, Simon Marlow wrote:
threadDelay is IO-only; there's no way to use threadDelay in an STM transaction. For example, if you want to wait for a TVar to go from Nothing to Just x with a timeout, you could do this:
readOrTimeout :: TVar (Maybe a) -> Int -> STM (Maybe a) readOrTimeout t secs = do timeout <- registerTimeout secs let check_timeout = do b <- readTVar timeout if b then return Nothing else retry check_t = do m <- readTVar t case m of Nothing -> retry Just x -> return x atomically $ check_timeout `orElse` check_t
Wouldn't it be readOrTimeout :: TVar (Maybe a) -> Int -> IO (Maybe a) ^^ ? Alternatively, it would be nice to have a new STM primitive: wailUntil :: ClockTime -> STM () so you would wait until some time-point passes, not for a number of time-units (waiting for a number of time-units wouldn't work because of retries). I think it could be efficiently implemented, wouldn't it? Best regards Tomasz -- I am searching for a programmer who is good at least in some of [Haskell, ML, C++, Linux, FreeBSD, math] for work in Warsaw, Poland