--- libraries/base/GHC/Enum.lhs.orig	2008-01-31 16:30:38.000000000 +0000
+++ libraries/base/GHC/Enum.lhs	2008-01-31 20:57:25.000000000 +0000
@@ -481,13 +481,19 @@
 			-- Watch out for y=maxBound; hence ==, not >
 	-- Be very careful not to have more than one "c"
 	-- so that when eftInfFB is inlined we can inline
-	-- whatver is bound to "c"
+	-- whatever is bound to "c"
 
 
 -----------------------------------------------------
 -- efdInt and efdtInt deal with [a,b..] and [a,b..c], which are much less common
--- so we are less elaborate.  The code is more complicated anyway, because
--- of worries about Int overflow, so we don't both with rules and deforestation
+-- so we are less elaborate.  The code is more complicated because of worries
+-- about Int overflow.
+
+{-# RULES
+"efdtInt"	[~1] forall x1 x2 y. efdtInt x1 x2 y = build (\ c n -> efdtIntFB c n x1 x2 y)
+"efdtIntUpList"	[1] efdtIntFB (:) [] = efdtInt
+ #-}
+
 
 efdInt :: Int# -> Int# -> [Int]
 -- [x1,x2..maxInt]
@@ -501,6 +507,12 @@
   | x2 >=# x1  = efdtIntUp x1 x2 y
   | otherwise  = efdtIntDn x1 x2 y
 
+{-# INLINE [0] efdtIntFB #-}
+efdtIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> Int# -> r
+efdtIntFB c n x1 x2 y
+  | x2 >=# x1  = efdtIntUpFB c n x1 x2 y
+  | otherwise  = efdtIntDnFB c n x1 x2 y
+
 efdtIntUp :: Int# -> Int# -> Int# -> [Int]
 efdtIntUp x1 x2 y	-- Be careful about overflow!
   | y <# x2    = if y <# x1 then [] else [I# x1]
@@ -516,7 +528,23 @@
 	        | otherwise = I# x : go_up (x +# delta)
     in 
     I# x1 : go_up x2
-  		 	
+
+efdtIntUpFB :: (Int -> r -> r) -> r -> Int# -> Int# -> Int# -> r
+efdtIntUpFB c n x1 x2 y	-- Be careful about overflow!
+  | y <# x2    = if y <# x1 then n else I# x1 `c` n
+  | otherwise 
+  = 	-- Common case: x1 < x2 <= y
+    let 
+	delta = x2 -# x1	
+	y' = y -# delta	
+	-- NB: x1 <= y'; hence y' is representable
+
+	-- Invariant: x <= y; and x+delta won't overflow
+        go_up x | x ># y'   = I# x `c` n
+	        | otherwise = I# x `c` go_up (x +# delta)
+    in 
+    I# x1 `c` go_up x2
+
 efdtIntDn :: Int# -> Int# -> Int# -> [Int]
 efdtIntDn x1 x2 y	-- x2 < x1
   | y ># x2    = if y ># x1 then [] else [I# x1]
@@ -532,5 +560,21 @@
 	        | otherwise = I# x : go_dn (x +# delta)
     in 
     I# x1 : go_dn x2
+
+efdtIntDnFB :: (Int -> r -> r) -> r -> Int# -> Int# -> Int# -> r
+efdtIntDnFB c n x1 x2 y	-- x2 < x1
+  | y ># x2    = if y ># x1 then n else I# x1 `c` n
+  | otherwise 
+  = 	-- Common case: x1 > x2 >= y
+    let 
+	delta = x2 -# x1	
+	y' = y -# delta	
+	-- NB: x1 <= y'; hence y' is representable
+
+	-- Invariant: x >= y; and x+delta won't overflow
+        go_dn x | x <# y'  = I# x `c` n
+	        | otherwise = I# x `c` go_dn (x +# delta)
+    in 
+    I# x1 `c` go_dn x2
 \end{code}