[Haskell-cafe] Are constructors strict?

Sebastian Fischer fischer at nii.ac.jp
Sat Jan 22 15:12:17 CET 2011

Hi Daryoush,

On Fri, Jan 21, 2011 at 7:52 PM, Daryoush Mehrtash <dmehrtash at gmail.com>wrote:

>  loop = MonadPlus m => m Bool
>  loop = loop
>> If we apply Just to loop as follows
>>  test2 :: MonadPlus m => m (Maybe Bool)
>  test2 = loop >>= return . Just
>> the evaluation of test2 does not terminate because >>= has to evaluate
>> loop. But this does not correctly reflect the behaviour in a functional
>> logic language like Curry. For example, if you have a function that checks
>> whether the outermost constructor of test2 is Just, the test is supposed to
>> be successful. In the naive model for non-determinism this is not the case.
> Do I have to have MonadPlus m or would any other Monad class work the same
> way?

I'm afraid, I don't quite get you question. Would you mind clarifying it
with an example?

Also, Jan, I don't understand your comment about continuation monads. Maybe
I am a bit numb today.. What property do you mean do continuation monads
have or not?

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