Fractions.hs

-----------------------------------------------------------------------------
--
-- Module      :  Math.Fractions
-- Copyright   :  (c) 2014-16 Brian W Bush
-- License     :  MIT
--
-- Maintainer  :  Brian W Bush <consult@brianwbush.info>
-- Stability   :  Experimental
-- Portability :  Portable
--
-- | Some special operations with fractions.
--
-----------------------------------------------------------------------------


{-# LANGUAGE Safe #-}


module Math.Fractions {-# DEPRECATED "This module will be removed in a future release." #-} (
-- * Functions
  fractions
, fractionsMaybe
) where


import Control.Arrow (second)
import Data.List.Util (regroup)
import Data.Maybe (mapMaybe)


-- | Apply a function to a list to extract keys with values that sum to unity.
fractions :: (Ord b, Fractional c) => (a -> (b, c)) -> [a] -> [(b, c)]
fractions extractor x =
  let
    x' = map (second sum) $ regroup $ map extractor x
    t = sum $ map snd x'
  in
    map (second (/ t)) x'


-- | Apply a function to a list to extract keys with values that sum to unity.
fractionsMaybe :: (Ord b, Fractional c) => (a -> Maybe (b, c)) -> [a] -> [(b, c)]           
fractionsMaybe = (fractions id .) . mapMaybe