{-# LANGUAGE Trustworthy #-} {-# LANGUAGE NoImplicitPrelude #-} ----------------------------------------------------------------------------- -- | -- Module : Data.Ord -- Copyright : (c) The University of Glasgow 2005 -- License : BSD-style (see the file libraries/base/LICENSE) -- -- Maintainer : libraries@haskell.org -- Stability : stable -- Portability : portable -- -- Orderings -- ----------------------------------------------------------------------------- module Data.Ord ( Ord(..), Ordering(..), Down(..), comparing, ) where import GHC.Base import GHC.Show import GHC.Read -- | -- > comparing p x y = compare (p x) (p y) -- -- Useful combinator for use in conjunction with the @xxxBy@ family -- of functions from "Data.List", for example: -- -- > ... sortBy (comparing fst) ... comparing :: (Ord a) => (b -> a) -> b -> b -> Ordering comparing p x y = compare (p x) (p y) -- | The 'Down' type allows you to reverse sort order conveniently. A value of type -- @'Down' a@ contains a value of type @a@ (represented as @'Down' a@). -- If @a@ has an @'Ord'@ instance associated with it then comparing two -- values thus wrapped will give you the opposite of their normal sort order. -- This is particularly useful when sorting in generalised list comprehensions, -- as in: @then sortWith by 'Down' x@ -- -- Provides 'Show' and 'Read' instances (/since: 4.7.0.0/). -- -- /Since: 4.6.0.0/ newtype Down a = Down a deriving (Eq, Show, Read) instance Ord a => Ord (Down a) where compare (Down x) (Down y) = y `compare` x