darcs patch: Add equating p x y = p x == p y
Nils Anders Danielsson
nad at cs.chalmers.se
Wed Oct 11 10:46:05 EDT 2006
On Wed, 11 Oct 2006, Duncan Coutts <duncan.coutts at worc.ox.ac.uk> wrote:
> Wed Oct 11 15:14:32 BST 2006 Duncan Coutts <duncan.coutts at worc.ox.ac.uk>
> * Add equating p x y = p x == p y
> Just as useful as the 'comparing' function from Data.Ord,
> but for cases where we check equality rather than ordering.
> Use like: groupBy (equating fst)
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)
--
/NAD
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