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|
{- percentages
-
- Copyright 2012 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Utility.Percentage (
Percentage,
percentage,
showPercentage
) where
import Data.Ratio
newtype Percentage = Percentage (Ratio Integer)
instance Show Percentage where
show = showPercentage 0
{- Normally the big number comes first. But 110% is allowed if desired. :) -}
percentage :: Integer -> Integer -> Percentage
percentage 0 _ = Percentage 0
percentage full have = Percentage $ have * 100 % full
{- Pretty-print a Percentage, with a specified level of precision. -}
showPercentage :: Int -> Percentage -> String
showPercentage precision (Percentage p)
| precision == 0 || remainder == 0 = go $ show int
| otherwise = go $ show int ++ "." ++ strip0s (show remainder)
where
go v = v ++ "%"
int :: Integer
(int, frac) = properFraction (fromRational p)
remainder = floor (frac * multiplier) :: Integer
strip0s = reverse . dropWhile (== '0') . reverse
multiplier :: Float
multiplier = 10 ** (fromIntegral precision)
|
