hledger/Amount.hs

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Haskell
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module Amount
where
import Utils
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import Types
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import Currency
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{-
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a simple amount is a currency, quantity pair:
$1
£-50
EUR 3.44
GOOG 500
1.5h
90m
0
a mixed amount is one or more simple amounts:
$50, EUR 3, AAPL 500
16h, $13.55, oranges 6
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currencies may be convertible or not (eg, currencies representing
non-money commodities). A mixed amount containing only convertible
currencies can be converted to a simple amount.
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arithmetic:
$1 - $5 = $-4
$1 + EUR 0.76 = $2
EUR0.76 + $1 = EUR 1.52
EUR0.76 - $1 = 0
($5, 2h) + $1 = ($6, 2h)
($50, EUR 3, AAPL 500) + ($13.55, oranges 6) = $67.51, AAPL 500, oranges 6
($50, EUR 3) * $-1 = $-53.96
($50, AAPL 500) * $-1 = error
-}
tests = runTestTT $ test [
show (dollars 1) ~?= "$1.00"
,show (hours 1) ~?= "1h" -- currently h1.00
,parseAmount "$1" ~?= dollars 1 -- currently 0
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]
nullamt = dollars 0
parseAmount :: String -> Amount
parseAmount s = nullamt
instance Show Amount where show = showAmountRounded
showAmountRounded :: Amount -> String
showAmountRounded (Amount c q p) =
(symbol c) ++ ({-punctuatethousands $ -}printf ("%."++show p++"f") q)
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showAmountRoundedOrZero :: Amount -> String
showAmountRoundedOrZero a@(Amount c _ _) =
let s = showAmountRounded a
noncurrency = drop (length $ symbol c)
nonnulls = filter (flip notElem "-+,.0")
iszero = (nonnulls $ noncurrency s) == ""
in if iszero then "0" else s
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punctuatethousands :: String -> String
punctuatethousands s =
sign ++ (punctuate int) ++ frac
where
(sign,num) = break isDigit s
(int,frac) = break (=='.') num
punctuate = reverse . concat . intersperse "," . triples . reverse
triples "" = []
triples s = [take 3 s] ++ (triples $ drop 3 s)
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instance Num Amount where
abs (Amount c q p) = Amount c (abs q) p
signum (Amount c q p) = Amount c (signum q) p
fromInteger i = Amount (getcurrency "$") (fromInteger i) amtintprecision
(+) = amountop (+)
(-) = amountop (-)
(*) = amountop (*)
-- problem: when an integer is converted to an amount it must pick a
-- precision, which we specify here (should be infinite ?). This can
-- affect amount arithmetic, in particular the sum of a list of amounts.
-- So, we may need to adjust the precision after summing amounts.
amtintprecision = 2
-- apply op to two amounts, adopting a's currency and lowest precision
amountop :: (Double -> Double -> Double) -> Amount -> Amount -> Amount
amountop op (Amount ac aq ap) b@(Amount _ _ bp) =
Amount ac (aq `op` (quantity $ toCurrency ac b)) (min ap bp)
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toCurrency :: Currency -> Amount -> Amount
toCurrency newc (Amount oldc q p) =
Amount newc (q * (conversionRate oldc newc)) p
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