Proposal: add new function "check" to Control.Monad

[Yitzchak Gale]

Jón Fairbairn wrote:
> Trac ticket #3453. Two week time frame.
> Add check function to Control.Monad
> check :: (MonadPlus m) => (a -> Bool) -> a -> m a

I remember needing this on a number of occasions.

>   mfilter = (join .) . liftM . check

I might write that as:

mFilter = (=<<) . check

That is an intriguing dual to filterM.

Regards,
Yitz