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'. I remember there was a lengthy discussion about the right name of 'on' and adding it to Data.Function. I had no need for that function because at this point I already had: https://hackage.haskell.org/package/utility-ht-0.0.14/docs/Data-Function-HT.... If I am right the short name 'on' was only adopted because it was not (automatically) exported by Prelude.