Control.Monad proposal: Add whenJust

[Henning Thielemann]

Am 10.05.2013 21:00, schrieb Gwern Branwen:

> Or expand hlint to catch whenJust like constructs and suggest use of
> the alternative? We already did that for when 'void' was added, put in
> a suggestion looking for things like '>> return ()'

I have suggested such rules to Neil Mitchell but he hesitated to 
recommend functions from Data.Foldable module.