[Haskell-beginners] How to display a time difference?
sean.ysl at gmail.com
Wed Mar 18 06:35:50 EDT 2009
The following code probably would do what I wanted to do.
play_move :: IORef Game_state -> IO ()
play_move game_state_ior = do
(_, state, _) <- readIORef game_state_ior
putStr "Playing AI: "
start_time <- getCurrentTime
let move = recommended_move state
end_time <- move `seq` (modifyIORef game_state_ior $!
update_interactive_from_move move) `seq` getCurrentTime
putStrLn $ show $ (diffUTCTime end_time start_time)
Due to the non-strictness of Haskell, the evaluation of the
expressions between start_time and end_time is deferred until there is
By using `seq` and ($!), the strictness can be forced.
On Wed, Mar 18, 2009 at 9:28 PM, Colin Paul Adams
<colin at colina.demon.co.uk> wrote:
>>>>>> "Yitzchak" == Yitzchak Gale <gale at sefer.org> writes:
> Yitzchak> Colin Paul Adams wrote:
> >> The code of the following routine is intended to indicate how
> >> long it takes for the computer to make a move. However the time
> >> is printed (as very close to zero) long before the move is
> >> made.
> Yitzchak> You are writing a thunk to the IORef. It only gets
> Yitzchak> computed later on when you read the value.
> Yitzchak> Try using:
> >> readIORef game_state_ior >>= evaluate
> >> . update_interactive_from_move move >>= writeIORef
> >> game_state_ior
> Yitzchak> evaluate is in Control.Exception.
> Still no joy with:
> play_move :: IORef Game_state -> IO ()
> play_move game_state_ior = do
> (_, state, _) <- readIORef game_state_ior
> putStr "Playing AI: "
> start_time <- getCurrentTime
> let move = recommended_move state
> readIORef game_state_ior >>=
> evaluate . update_interactive_from_move move >>=
> writeIORef game_state_ior
> end_time <- getCurrentTime
> putStrLn $ show $ (diffUTCTime end_time start_time)
> Colin Adams
> Preston Lancashire
> Beginners mailing list
> Beginners at haskell.org
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