On Sat, May 30, 2009 at 10:32 PM, Cetin Sert <
cetin.sert@gmail.com> wrote:
Thank you for your reply, I'd come up with the following:
timed :: Int → IO a → b → IO (Either b a)
timed max act def = do
r ← new
t ← forkIO $ do
a ← act
r ≔ Right a
s ← forkIO $ do
wait max
e ← em r
case e of
True → do
kill t
r ≔ Left def
False → return ()
takeMVar r
---------------------
*Network.Port.Scan> timed 500 (wait 50000 >> return 0) 'x'
Left 'x'
*Network.Port.Scan> timed 500000 (wait 50000 >> return 0) 'x'
Right 0
---------------------
before reading your reply:
timed timeout act fallback = do
res <- newEmptyMVar
tid <- forkIO $ act >>= writeMVar res
threadDelay timeout
stillRunning <- isEmptyMVar res
if stillRunning then killThread tid >> return fallback else takeMVar res
---------------------
*Network.Port.Scan> timed2 500 (wait 50000 >> return 0) 'x'
<interactive>:1:33:
No instance for (Num Char)
arising from the literal `0' at <interactive>:1:33
Possible fix: add an instance declaration for (Num Char)
In the first argument of `return', namely `0'
In the second argument of `(>>)', namely `return 0'
In the second argument of `timed2', namely
`(wait 50000 >> return 0)'
Right, I forgot about the "Either" bit so you'd have to make sure the action's result and the default has the same type (or modify it to return an Either).
--
Sebastian Sylvan
+44(0)7857-300802
UIN: 44640862