From 4cb2a03f7f07c0b065e1540fd083c8ec4f8bb89b Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Mon, 18 Nov 2019 17:22:42 -0800
Subject: [PATCH] ;lib: more docs for unifyMixedAmount

[ci skip]
---
 hledger-lib/Hledger/Reports/BalanceReport.hs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hledger-lib/Hledger/Reports/BalanceReport.hs b/hledger-lib/Hledger/Reports/BalanceReport.hs
index 9730950f4..1afeefe7f 100644
--- a/hledger-lib/Hledger/Reports/BalanceReport.hs
+++ b/hledger-lib/Hledger/Reports/BalanceReport.hs
@@ -196,6 +196,10 @@ brNegate (is, tot) = (map brItemNegate is, -tot)
     brItemNegate (a, a', d, amt) = (a, a', d, -amt)
 
 -- | Helper to unify a MixedAmount to a single commodity value.
+-- Like normaliseMixedAmount, this consolidates amounts of the same commodity
+-- and discards zero amounts; but this one insists on simplifying to
+-- a single commodity, and will throw a program-terminating error if
+-- this is not possible.
 unifyMixedAmount :: MixedAmount -> Amount
 unifyMixedAmount mixedAmount = foldl combine (num 0) (amounts mixedAmount)
   where