    {-# OPTIONS -Wall -Werror #-}

    -- #hide
    module Data.Time.Calendar.Days
    (
    	-- * Days
    	Day(..),addDays,diffDays
    ) where

    -- | The Modified Julian Day is a standard count of days, with zero being the day 1858-11-17.
    newtype Day = ModifiedJulianDay {toModifiedJulianDay :: Integer} deriving (Eq,Ord)

    -- necessary because H98 doesn't have "cunning newtype" derivation
    instance Enum Day where
    	succ (ModifiedJulianDay a) = ModifiedJulianDay (succ a)
    	pred (ModifiedJulianDay a) = ModifiedJulianDay (pred a)
    	toEnum = ModifiedJulianDay . toEnum
    	fromEnum (ModifiedJulianDay a) = fromEnum a
    	enumFrom (ModifiedJulianDay a) = fmap ModifiedJulianDay (enumFrom a)
    	enumFromThen (ModifiedJulianDay a) (ModifiedJulianDay b) = fmap ModifiedJulianDay (enumFromThen a b)
    	enumFromTo (ModifiedJulianDay a) (ModifiedJulianDay b) = fmap ModifiedJulianDay (enumFromTo a b)
    	enumFromThenTo (ModifiedJulianDay a) (ModifiedJulianDay b) (ModifiedJulianDay c) = fmap ModifiedJulianDay (enumFromThenTo a b c)

    addDays :: Integer -> Day -> Day
    addDays n (ModifiedJulianDay a) = ModifiedJulianDay (a + n)

    diffDays :: Day -> Day -> Integer
    diffDays (ModifiedJulianDay a) (ModifiedJulianDay b) = a - b

    {-
    instance Show Day where
    	show (ModifiedJulianDay d) = "MJD " ++ (show d)

    -- necessary because H98 doesn't have "cunning newtype" derivation
    instance Num Day where
    	(ModifiedJulianDay a) + (ModifiedJulianDay b) = ModifiedJulianDay (a + b)
    	(ModifiedJulianDay a) - (ModifiedJulianDay b) = ModifiedJulianDay (a - b)
    	(ModifiedJulianDay a) * (ModifiedJulianDay b) = ModifiedJulianDay (a * b)
    	negate (ModifiedJulianDay a) = ModifiedJulianDay (negate a)
    	abs (ModifiedJulianDay a) = ModifiedJulianDay (abs a)
    	signum (ModifiedJulianDay a) = ModifiedJulianDay (signum a)
    	fromInteger = ModifiedJulianDay

    instance Real Day where
    	toRational (ModifiedJulianDay a) = toRational a

    instance Integral Day where
    	toInteger (ModifiedJulianDay a) = toInteger a
    	quotRem (ModifiedJulianDay a) (ModifiedJulianDay b) = (ModifiedJulianDay c,ModifiedJulianDay d) where
    		(c,d) = quotRem a b
    -}