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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I doesn't seems to be easy, either with deepseq-th or deepseq-generic... With deepseq-generic, the derivation of Generic doesn't work because I'm using a GATD. It says *"NewVar must be a vanilla data constructor"*. For deepseq-th, I have this error: *deriveNFData: 'forall' not supported in constructor declaration* I have some complex data constructor... So it looks like both deepseq-th and deepseq-generic are out of the game :(( On Mon, Jan 13, 2014 at 12:08 AM, Erik de Castro Lopo wrote:

James ‘Twey’ Kay wrote:

...

You can (probably) automatically derive it via Template Haskell using the deepseq-th package:

{-# LANGUAGE TemplateHaskell #-} import Control.DeepSeq.TH

data MyState = ...

$(deriveNFData ''MyState)

In most cases where you think

You should probably try the deepseq-generics package before you try deepseq-th.

The generics version was suggested to me by the author of the TH version, Herbert Valerio Riedel. It seems to be just as fast as the TH version and doesn't require TH.

Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe