[Haskell-cafe] different behaviours with or without putStrLn
carter.schonwald at gmail.com
Sun Jan 19 23:00:57 UTC 2014
*instance NFData a => NFData (MyGADT (Maybe a) )*
On Sunday, January 19, 2014, Corentin Dupont <corentin.dupont at gmail.com>
> I've tried the make an instance of NFData for all types, although I have a
> problem with the GATD:
> *data MyGADT a where MyField :: b -> MyGADT (Maybe b) instance NFData a
> => NFData (MyGADT a) where rnf (MyField b) = (rnf b)*
> Gives me :
> Could not deduce (NFData b) arising from a use of `rnf'
> from the context (NFData a)
> Which I understand (that's because a ~ *Maybe b *and not* a ~ b *due to
> the declaration of *MyField b *being of type *MyGADT (Maybe b)*)
> *But I have no idea how to solve that?? *
> > wrote:
>> On Sun, Jan 12, 2014 at 6:44 PM, Corentin Dupont <
>> 'corentin.dupont at gmail.com');>> wrote:
>>> One question:
>>> Since it works with putStrLn, can I simulate the behaviour of putStrLn
>>> without actually... printing anything? As a workaround...
>> Worst case, open a handle on /dev/null and hPutStr to it.
>> I'd probably try to figure out how to write appropriate NFData instances,
>> brandon s allbery kf8nh sine nomine
>> 'ballbery at sinenomine.net');>
>> unix, openafs, kerberos, infrastructure, xmonad
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