new MonadRandom instance; and maintainership
Felipe Almeida Lessa
felipe.lessa at gmail.com
Fri Apr 26 00:22:36 CEST 2013
Wouldn't Alternative lead to the same bug?
On Thu, Apr 25, 2013 at 7:02 PM, Sjoerd Visscher <sjoerd at w3future.com> wrote:
> Maybe a derived Alternative instance for RandT still makes sense?
> On Apr 25, 2013, at 8:28 PM, Brent Yorgey <byorgey at seas.upenn.edu> wrote:
>> On Thu, Apr 25, 2013 at 10:47:57AM -0400, Brent Yorgey wrote:
>>> On Wed, Apr 24, 2013 at 02:38:01PM -0400, Brent Yorgey wrote:
>>>> Hi all,
>>>> I would like to add a derived MonadPlus instance for both Rand and
>>>> RandT. Also, since it seems that MonadRandom has no maintainer I
>>>> propose to take on its maintainership. Any
>>>> comments/objections/etc. welcome.
>>> Also, ignore what I said about deriving an instance for Rand, that
>>> does not make any sense. However, adding an instance for RandT does
>>> still make sense. A repository with the changes is here:
>>> I'll upload in a few days if no one objects.
>> Puzzle time! Can you explain the semantics of the following code
>> (given a derived MonadPlus instance for RandT)?
>> maybeFail :: RandT StdGen Maybe ()
>> maybeFail = do
>> r <- getRandomR (0, 1 :: Double)
>> guard (r < 1/2)
>> succeed :: RandT StdGen Maybe ()
>> succeed = maybeFail `mplus` succeed
>> I therefore rescind my proposal to add a MonadPlus instance for
>> RandT. However, I still volunteer to be the maintainer. =)
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