On Tue, 10 Sep 2019, David Feuer wrote:

> Every time I reach for Data.Function.on, I feel like a total dolt for having to import a module to get a function
> whose implementation is barely longer than the import. And it's a really good function too! Can we please add it
> to the Prelude?
>   on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
>   (.*.) `on` f = \x y -> f x .*. f y

Most of the time I would use this I can use the more specific 'equating'
and 'comparing'.