darcs patch: Add equating p x y = p x == p y

[Samuel Bronson]

On 10/11/06, Nils Anders Danielsson <nad at cs.chalmers.se> wrote:

> Instead of adding 'comparing', 'equating' etc., I suggest that you add
> the more general 'on', which is just as easy to use. ('on' has been
> mentioned on the lists a couple of times before.)
>
>   (*) `on` f = \x y -> f x * f y
>
>   groupBy ((==) `on` fst)
>   sortBy (compare `on` snd)
>   maximumBy (customCompare `on` f)

Oh, oops. I meant to send this to the list the *first* time... so, um,
where is the patch for this?