From 1e6ad7ab1d081f69cfb09eac24f2a47536080fff Mon Sep 17 00:00:00 2001
From: simonpj <unknown>
Date: Wed, 12 Oct 2005 10:57:40 +0000
Subject: [PATCH] [project @ 2005-10-12 10:57:40 by simonpj] Comments

---
 GHC/Arr.lhs |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/GHC/Arr.lhs b/GHC/Arr.lhs
index c5e945f..0b29db0 100644
--- a/GHC/Arr.lhs
+++ b/GHC/Arr.lhs
@@ -75,12 +75,16 @@ class (Ord a) => Ix a where
     unsafeRangeSize     :: (a,a) -> Int
 
 	-- Must specify one of index, unsafeIndex
-    index b i | inRange b i = unsafeIndex b i
+    index b i | inRange b i = unsafeIndex b i	
 	      | otherwise   = error "Error in array index"
     unsafeIndex b i = index b i
 
     rangeSize b@(_l,h) | inRange b h = unsafeIndex b h + 1
-		       | otherwise   = 0
+		       | otherwise   = 0	-- This case is only here to
+						-- check for an empty range
+	-- NB: replacing (inRange b h) by (l <= h) fails for
+	--     tuples.  E.g.  (1,2) <= (2,1) but the range is empty
+
     unsafeRangeSize b@(_l,h) = unsafeIndex b h + 1
 \end{code}
 
-- 
1.7.10.4