Re: [Haskell-cafe] different behaviours with or without putStrLn

You can (probably) automatically derive it via Template Haskell using the deepseq-th package: {-# LANGUAGE TemplateHaskell #-} import Control.DeepSeq.TH data MyState = ... $(deriveNFData ''MyState) On 2014-01-12 22:26, Corentin Dupont wrote:

deepseq seems interresting (didn't know it). Do I have to create instances of NFData [2] for all my types? Too bad it's not derivable.

On Sun, Jan 12, 2014 at 11:10 PM, Ben Foppa wrote:

...

Depending on the kind of state, WHNF may not be enough - have you tried with deepseq?

On Sun, Jan 12, 2014 at 5:07 PM, Corentin Dupont wrote:

...

Hi guys, I'm experimenting different behaviours with or without a "putStrLn"! :(

Basically, with the following code, I want the evaluation to really happen on the "evaluate".

I found out that it doesn't: it is evaluated elsewhere (I don't know where).

If I put a putStrLn (commented below), the evaluation really happens there.

execCommand :: (TVar MyState) -> StateT MyState IO () -> IO () execCommand ts sm = do    s <- atomically $ readTVar ts    s' <- execStateT sm s    s'' <- evaluate s'          --evaluation should happen here, but it doesn't    --putStrLn $ displayMulti $ _multi s''    atomically $ writeTVar ts s''

To give you more context, I have a state that, when evaluated, might not terminate. So I added a watchdog (like in mueval), that will kill the thread in case the evaluation doesn't terminate.

That's why I need to be sure of where the evaluation takes place.

Thanks!

Corentin

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