[Haskell-cafe] different behaviours with or without putStrLn

[Corentin Dupont]

deepseq seems interresting (didn't know it).
Do I have to create instances of
NFData<http://hackage.haskell.org/package/deepseq-1.3.0.2/docs/Control-DeepSeq.html#t:NFData>for
all my types? Too bad it's not derivable.

On Sun, Jan 12, 2014 at 11:10 PM, Ben Foppa <benjamin.foppa at gmail.com>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 <
> corentin.dupont at gmail.com> 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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>>
>
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