109 lines
3.2 KiB
Haskell
109 lines
3.2 KiB
Haskell
{-|
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An 'Amount' is some quantity of money, shares, or anything else.
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A simple amount is a currency, quantity pair (where currency can be anything):
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@
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$1
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£-50
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EUR 3.44
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GOOG 500
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1.5h
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90apples
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0
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@
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A mixed amount (not yet implemented) is one or more simple amounts:
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@
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$50, EUR 3, AAPL 500
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16h, $13.55, oranges 6
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@
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Currencies may be convertible or not (eg, currencies representing
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non-money commodities). A mixed amount containing only convertible
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currencies can be converted to a simple amount. Arithmetic examples:
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@
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$1 - $5 = $-4
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$1 + EUR 0.76 = $2
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EUR0.76 + $1 = EUR 1.52
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EUR0.76 - $1 = 0
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($5, 2h) + $1 = ($6, 2h)
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($50, EUR 3, AAPL 500) + ($13.55, oranges 6) = $67.51, AAPL 500, oranges 6
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($50, EUR 3) * $-1 = $-53.96
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($50, AAPL 500) * $-1 = error
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@
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-}
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module Ledger.Amount
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where
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import Ledger.Utils
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import Ledger.Types
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import Ledger.Currency
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tests = runTestTT $ test [
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show (dollars 1) ~?= "$1.00"
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,show (hours 1) ~?= "1h" -- currently h1.00
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]
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instance Show Amount where show = showAmountRounded
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-- | Get the string representation of an amount, rounded to its native precision.
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-- Unlike ledger, we show the decimal digits even if they are all 0, and
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-- we always show currency symbols on the left.
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showAmountRounded :: Amount -> String
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showAmountRounded (Amount c q p) =
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(symbol c) ++ ({-punctuatethousands $ -}printf ("%."++show p++"f") q)
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-- | Get the string representation of an amount, rounded, or showing just "0" if it's zero.
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showAmountRoundedOrZero :: Amount -> String
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showAmountRoundedOrZero a
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| isZeroAmount a = "0"
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| otherwise = showAmountRounded a
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-- | is this amount zero, when displayed with its given precision ?
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isZeroAmount :: Amount -> Bool
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isZeroAmount a@(Amount c _ _) = nonzerodigits == ""
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where
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nonzerodigits = filter (flip notElem "-+,.0") quantitystr
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quantitystr = withoutcurrency $ showAmountRounded a
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withoutcurrency = drop (length $ symbol c)
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punctuatethousands :: String -> String
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punctuatethousands s =
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sign ++ (punctuate int) ++ frac
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where
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(sign,num) = break isDigit s
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(int,frac) = break (=='.') num
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punctuate = reverse . concat . intersperse "," . triples . reverse
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triples "" = []
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triples s = [take 3 s] ++ (triples $ drop 3 s)
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instance Num Amount where
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abs (Amount c q p) = Amount c (abs q) p
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signum (Amount c q p) = Amount c (signum q) p
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fromInteger i = Amount (getcurrency "") (fromInteger i) defaultprecision
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(+) = amountop (+)
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(-) = amountop (-)
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(*) = amountop (*)
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-- amounts converted from integers will have a default precision, and the
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-- null currency.
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defaultprecision = 2
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-- | Apply a binary arithmetic operator to two amounts, converting to the
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-- second one's currency and adopting the lowest precision. (Using the
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-- second currency means that folds (like sum [Amount]) will preserve the
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-- currency.)
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amountop :: (Double -> Double -> Double) -> Amount -> Amount -> Amount
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amountop op a@(Amount ac aq ap) b@(Amount bc bq bp) =
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Amount bc ((quantity $ toCurrency bc a) `op` bq) (min ap bp)
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toCurrency :: Currency -> Amount -> Amount
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toCurrency newc (Amount oldc q p) =
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Amount newc (q * (conversionRate oldc newc)) p
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nullamt = Amount (getcurrency "") 0 2
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