From c42496b1341b4ccb546d1e579ef18d2b5e7d10d8 Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Tue, 27 Jul 2010 23:20:20 +0000
Subject: [PATCH] sign testing for amounts

---
 hledger-lib/Hledger/Data/Amount.hs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/hledger-lib/Hledger/Data/Amount.hs b/hledger-lib/Hledger/Data/Amount.hs
index adfd26e6d..8cc6170da 100644
--- a/hledger-lib/Hledger/Data/Amount.hs
+++ b/hledger-lib/Hledger/Data/Amount.hs
@@ -153,6 +153,10 @@ isReallyZeroAmount :: Amount -> Bool
 isReallyZeroAmount = null . filter (`elem` "123456789") . printf ("%."++show zeroprecision++"f") . quantity
     where zeroprecision = 8
 
+-- | Is this amount negative ? The price is ignored.
+isNegativeAmount :: Amount -> Bool
+isNegativeAmount Amount{quantity=q} = q < 0
+
 -- | Access a mixed amount's components.
 amounts :: MixedAmount -> [Amount]
 amounts (Mixed as) = as
@@ -166,6 +170,13 @@ isZeroMixedAmount = all isZeroAmount . amounts . normaliseMixedAmount
 isReallyZeroMixedAmount :: MixedAmount -> Bool
 isReallyZeroMixedAmount = all isReallyZeroAmount . amounts . normaliseMixedAmount
 
+-- | Is this mixed amount negative, if it can be normalised to a single commodity ?
+isNegativeMixedAmount :: MixedAmount -> Maybe Bool
+isNegativeMixedAmount m = case as of [a] -> Just $ isNegativeAmount a
+                                     _   -> Nothing
+    where
+      as = amounts $ normaliseMixedAmount m
+
 -- | Is this mixed amount "really" zero, after converting to cost
 -- commodities where possible ?
 isReallyZeroMixedAmountCost :: MixedAmount -> Bool