forgot to add Amount module

Amount.hs

@@ -0,0 +1,114 @@
+module Amount
+where
+import Utils
+import BasicTypes
+
+{- 
+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
+
+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 "$1"   ~?= dollars 1 -- currently 0
+        ]
+
+-- currency
+
+data Currency = Currency {
+      symbol :: String,
+      rate :: Double -- relative to the dollar
+    } deriving (Eq,Show)
+
+currencies = 
+    [
+     Currency "$"   1        
+    ,Currency "EUR" 0.760383 
+    ,Currency "£"   0.512527 
+    ,Currency "h"   60         -- hours
+    ,Currency "m"   1          -- minutes
+    ]
+
+getcurrency :: String -> Currency
+getcurrency s = head $ [(Currency symbol rate) | (Currency symbol rate) <- currencies, symbol==s]
+
+-- convenience
+dollars = Amount $ getcurrency "$"
+euro    = Amount $ getcurrency "EUR"
+pounds  = Amount $ getcurrency "£"
+hours   = Amount $ getcurrency "h"
+minutes = Amount $ getcurrency "m"
+
+conversionRate :: Currency -> Currency -> Double
+conversionRate oldc newc = (rate newc) / (rate oldc)
+
+
+-- amount    
+
+data Amount = Amount {
+                      currency :: Currency,
+                      quantity :: Double
+                     } deriving (Eq)
+
+instance Show Amount where show = showAmountRoundedOrZero
+
+nullamt = dollars 0
+
+parseAmount :: String -> Amount
+parseAmount s = nullamt
+
+showAmountRoundedOrZero :: Amount -> String
+showAmountRoundedOrZero (Amount cur qty) =
+    let rounded = printf "%.2f" qty in
+    case rounded of
+      "0.00"    -> "0"
+      "-0.00"   -> "0"
+      otherwise -> (symbol cur) ++ rounded
+
+instance Num Amount where
+    abs (Amount c q) = Amount c (abs q)
+    signum (Amount c q) = Amount c (signum q)
+    fromInteger i = Amount (getcurrency "$") (fromInteger i)
+    (+) = amountAdd
+    (-) = amountSub
+    (*) = amountMul
+Amount ac aq `amountAdd` b = Amount ac (aq + (quantity $ toCurrency ac b))
+Amount ac aq `amountSub` b = Amount ac (aq - (quantity $ toCurrency ac b))
+Amount ac aq `amountMul` b = Amount ac (aq * (quantity $ toCurrency ac b))
+
+toCurrency :: Currency -> Amount -> Amount
+toCurrency newc (Amount oldc q) =
+    Amount newc (q * (conversionRate oldc newc))
+
+
+-- mixed amounts
+
+--data MixedAmount = MixedAmount [Amount] deriving (Eq,Ord)
+