+1

On Tue, Sep 10, 2019, 5:53 PM David Feuer <david.feuer@gmail.com> 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

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