[Haskell-cafe] different behaviours with or without putStrLn

Corentin Dupont corentin.dupont at gmail.com
Sun Jan 19 22:22:33 UTC 2014

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??*



On Mon, Jan 13, 2014 at 1:10 AM, Brandon Allbery <allbery.b at gmail.com>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,
> though.
> --
> brandon s allbery kf8nh                               sine nomine
> associates
> allbery.b at gmail.com
> ballbery at sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad
> http://sinenomine.net
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