On Wed, 10 Apr 2019, James Ashwell wrote: > This would mimic the behaviour of Control.Monad.when for monoids rather than applicatives. > > mwhen :: Monoid m => Bool -> m -> m > mwhen b a > | b = a > | otherwise = mempty https://hackage.haskell.org/package/utility-ht-0.0.14/docs/Data-Monoid-HT.html#v:when