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