Bulat,
yes, with both variants. actually, second one should be easier to implement and understand. you should look into unsafeInterleaveIO section of http://haskell.org/haskellwiki/IO_inside
This seems to do what I want, and unless I'm overlooking something it feels very straight-forward: hGetContentsTimeout :: Handle -> Int -> IO String hGetContentsTimeout h t = do hSetBuffering stdin NoBuffering ready <- hWaitForInput h t if (not ready) then return [] else do c <- hGetChar h s <- unsafeInterleaveIO (hGetContentsTimeout h t) return (c:s) This is not extensivly tested, but applying my parser to the string returned by hGetContentsTimeout behaves precisely as I wanted: It returns a match as soon as it is available, and fails if it is not seen within t ms. Thanks for your help! - Scott