diff --git a/Data/Array/Repa/Eval/Reduction.hs b/Data/Array/Repa/Eval/Reduction.hs
--- a/Data/Array/Repa/Eval/Reduction.hs
+++ b/Data/Array/Repa/Eval/Reduction.hs
@@ -153,7 +153,7 @@
    {-# INLINE iter #-}
    iter !i !z 
     | 1# <- i >=# end  = z 
-    | otherwise        = iter (i +# 1#) (f i `c` z)
+    | otherwise        = iter (i +# 1#) (z `c` f i)
 
 
 {-# INLINE [0] reduceInt #-}
@@ -170,7 +170,7 @@
    {-# INLINE iter #-}
    iter !i !z 
     | 1# <- i >=# end   = z 
-    | otherwise         = iter (i +# 1#) (f i `c` z)
+    | otherwise         = iter (i +# 1#) (z `c` f i)
 
 
 {-# INLINE [0] reduceFloat #-}
@@ -187,7 +187,7 @@
    {-# INLINE iter #-}
    iter !i !z 
     | 1# <- i >=# end   = z 
-    | otherwise         = iter (i +# 1#) (f i `c` z)
+    | otherwise         = iter (i +# 1#) (z `c` f i)
 
 
 {-# INLINE [0] reduceDouble #-}
@@ -204,7 +204,7 @@
    {-# INLINE iter #-}
    iter !i !z 
     | 1# <- i >=# end   = z 
-    | otherwise         = iter (i +# 1#) (f i `c` z)
+    | otherwise         = iter (i +# 1#) (z `c` f i)
 
 
 {-# INLINE unboxInt #-}
diff --git a/Data/Array/Repa/Operators/Reduction.hs b/Data/Array/Repa/Operators/Reduction.hs
--- a/Data/Array/Repa/Operators/Reduction.hs
+++ b/Data/Array/Repa/Operators/Reduction.hs
@@ -24,6 +24,15 @@
 -- | Sequential reduction of the innermost dimension of an arbitrary rank array.
 --
 --   Combine this with `transpose` to fold any other dimension.
+--
+--   Elements are reduced in the order of their indices, from lowest to highest.
+--   Applications of the operator are associatied arbitrarily.
+--
+--   >>> let c 0 x = x; c x 0 = x; c x y = y
+--   >>> let a = fromListUnboxed (Z :. 2 :. 2) [1,2,3,4] :: Array U (Z :. Int :. Int) Int
+--   >>> foldS c 0 a
+--   AUnboxed (Z :. 2) (fromList [2,4])
+--
 foldS   :: (Shape sh, Source r a, Elt a, Unbox a)
         => (a -> a -> a)
         -> a
@@ -49,6 +58,15 @@
 --   example @0@ is neutral with respect to @(+)@ as @0 + a = a@.
 --   These restrictions are required to support parallel evaluation, as the
 --   starting element may be used multiple times depending on the number of threads.
+--
+--   Elements are reduced in the order of their indices, from lowest to highest.
+--   Applications of the operator are associatied arbitrarily.
+--
+--   >>> let c 0 x = x; c x 0 = x; c x y = y
+--   >>> let a = fromListUnboxed (Z :. 2 :. 2) [1,2,3,4] :: Array U (Z :. Int :. Int) Int
+--   >>> foldP c 0 a
+--   AUnboxed (Z :. 2) (fromList [2,4])
+--
 foldP   :: (Shape sh, Source r a, Elt a, Unbox a, Monad m)
         => (a -> a -> a)
         -> a
@@ -79,6 +97,9 @@
 -- foldAll --------------------------------------------------------------------
 -- | Sequential reduction of an array of arbitrary rank to a single scalar value.
 --
+--   Elements are reduced in row-major order. Applications of the operator are
+--   associated arbitrarily.
+--
 foldAllS :: (Shape sh, Source r a, Elt a, Unbox a)
 	=> (a -> a -> a)
 	-> a
@@ -102,6 +123,10 @@
 --   for example @0@ is neutral with respect to @(+)@ as @0 + a = a@.
 --   These restrictions are required to support parallel evaluation, as the
 --   starting element may be used multiple times depending on the number of threads.
+--
+--   Elements are reduced in row-major order. Applications of the operator are
+--   associated arbitrarily.
+--
 foldAllP 
         :: (Shape sh, Source r a, Elt a, Unbox a, Monad m)
 	=> (a -> a -> a)
diff --git a/repa.cabal b/repa.cabal
--- a/repa.cabal
+++ b/repa.cabal
@@ -1,5 +1,5 @@
 Name:                repa
-Version:             3.2.5.1
+Version:             3.3.1.1
 License:             BSD3
 License-file:        LICENSE
 Author:              The DPH Team