better zero amount checking

Ledger/Amount.hs

@@ -60,12 +60,17 @@ showAmountRounded (Amount c q p) =
     (symbol c) ++ ({-punctuatethousands $ -}printf ("%."++show p++"f") q)
 
 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
+showAmountRoundedOrZero a
+    | isZeroAmount a = "0"
+    | otherwise = showAmountRounded a
+
+-- | is this amount zero, when displayed with its given precision ?
+isZeroAmount :: Amount -> Bool
+isZeroAmount a@(Amount c _ _) = nonzerodigits == ""
+    where
+      nonzerodigits = filter (flip notElem "-+,.0") quantitystr
+      quantitystr = withoutcurrency $ showAmountRounded a
+      withoutcurrency = drop (length $ symbol c)
 
 punctuatethousands :: String -> String
 punctuatethousands s =

Ledger/Entry.hs

@@ -37,9 +37,8 @@ showEntryDescription e = (showDate $ edate e) ++ " " ++ (showDescription $ edesc
 showDate d = printf "%-10s" d
 showDescription s = printf "%-20s" (elideRight 20 s)
 
--- | quick & dirty: checks entry's 0 balance only to 8 places
 isEntryBalanced :: Entry -> Bool
-isEntryBalanced = ((0::Double)==) . read . printf "%0.8f" . quantity . sumLedgerTransactions . etransactions
+isEntryBalanced = isZeroAmount . sumLedgerTransactions . etransactions
 
 autofillEntry :: Entry -> Entry
 autofillEntry e@(Entry _ _ _ _ _ ts _) =