The monoid-subclasses packages provides a MonoidNull class that you could
use:
http://hackage.haskell.org/package/monoid-subclasses-0.4.6.1/docs/Data-Monoi...
Am Sa., 25. Mai 2019 um 07:56 Uhr schrieb Dr.Koster
It's often useful to have a generalized null/unit test, e.g. to check if a monadic stream `m a` reaches EOF. A workaround is to use `Eq a, Monoid a` constraint and use `== mempty` test. But this is no only inefficient for some type, but also impossible for some monoids, such as Builders.
I propose add this test `isEmpty :: a -> Bool` to `Monoid`, to provide the ability to check if a value is the unit value.
Cheers Han Dong~ _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries