On 09/02/11 15:34, Krzysztof Skrzętnicki wrote:

Hello Cafe,

Here is a simple program that yields strange results:

module Main where

import Control.Concurrent
import Control.Concurrent.Chan
import Control.Monad

main = do
c <- newChan
writeChan c 1
forkIO $ forever $ do
i <- readChan c
print ("forkio",i)
isEmptyChan c >>= print

Now, this is strange thing: we put single element into the channel. We take it out.

What your program does is put a single element into the channel, and then *repeatedly* try to take one out (notice the forever you have in there!). Judging by the results, the program deadlocks, which seems like a reasonable outcome to me.

Thanks,

Neil.