[project @ 2005-10-12 10:57:40 by simonpj]

Comments

diff --git a/GHC/Arr.lhs b/GHC/Arr.lhs
index c5e945f..0b29db0 100644 (file)
--- 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}