Re: [Haskell-beginners] How to display a time difference?

Hi Colin 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 a need. By using `seq` and ($!), the strictness can be forced. Sean On Wed, Mar 18, 2009 at 9:28 PM, Colin Paul Adams wrote:

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"Yitzchak" == Yitzchak Gale 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@haskell.org http://www.haskell.org/mailman/listinfo/beginners

-- Sean Lee PhD Student Programming Language and Systems Research Group School of Computer Science and Engineering University of New South Wales http://www.cse.unsw.edu.au/~seanl