Util.hs

-----------------------------------------------------------------------------
--
-- Module      :  Data.Function.Util
-- Copyright   :  (c) 2014-16 Brian W Bush
-- License     :  MIT
--
-- Maintainer  :  Brian W Bush <consult@brianwbush.info>
-- Stability   :  Stable
-- Portability :  Portable
--
-- | Utilities related to "Data.Function".
--
-----------------------------------------------------------------------------


{-# LANGUAGE Safe #-}


module Data.Function.Util (
-- * Constant boolean functions
  always
, never
-- * Functions on second entries in pairs
, sndNegater
, sndCounter
, sndSummer
) where


import Control.Arrow (second)


-- | Always true.
always :: a -> Bool
always = const True


-- | Always false.
never :: a -> Bool
never = const False


-- | Negate the second entry in a pair.
sndNegater :: Num b => (a, b) -> (a, b)
sndNegater = second negate


-- | Measure the length of the second entry in a pair.
sndCounter :: (a, [b]) -> (a, Int)
sndCounter = second length


-- | Sum the values of the second entry in a pair.
sndSummer :: Num b => (a, [b]) -> (a, b)
sndSummer = second sum