Re: Proposal: Add Data.Monoid.mwhen :: Monoid m => Bool -> m -> m

On 10-04-19 14:04, Mario Blažević wrote:

On 2019-04-10 11:36 a.m., 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

Or shorter

mwhen = bool (const mempty) id

I'd rather construct the right-hand side than memorize the left, so -1 from me. Exactly, monoids usually don't operate on their own context as Monad/Applicatives do. It is better to see them as pure values dependent on `Bool`, for which Data.Bool.bool is a perfect function. Also the rhs is clearer and easier to remember.

A -1 from me. -- -- Rubén -- pgp: 4EE9 28F7 932E F4AD