diff --git a/quiver.cabal b/quiver.cabal
--- a/quiver.cabal
+++ b/quiver.cabal
@@ -1,5 +1,5 @@
 name:               quiver
-version:            1.1.2
+version:            1.1.3
 synopsis:           Quiver finite stream processing library
 homepage:           https://github.com/zadarnowski/quiver
 category:           Control
diff --git a/src/Control/Quiver/SP.lhs b/src/Control/Quiver/SP.lhs
--- a/src/Control/Quiver/SP.lhs
+++ b/src/Control/Quiver/SP.lhs
@@ -23,7 +23,7 @@
 >   spconsume,
 >   spfetch, spemit, (>:>), (>>?), (>>!),
 >   sppure, spid, spconcat, spfilter,
->   spfold, spfold', spfoldl, spfoldl', spfoldr, spfoldr',
+>   spfold, spfold', spfoldl, spfoldl', spfoldr,
 >   sptraverse, sptraverse_,
 >   spevery,
 >   spforever,
@@ -52,15 +52,15 @@
 
 > -- | A producer version of a simple processor.
 
-> type SProducer b f e = forall a . SP a b f e
+> type SProducer b f e = forall b' . Producer b b' f (SPResult e)
 
 > -- | A consumer version of a simple processor.
 
-> type SConsumer a f e = forall b . SP a b f e
+> type SConsumer a f e = Consumer () a f (SPResult e)
 
 > -- | An effect version of a simple processor.
 
-> type SEffect f e = forall a b . SP a b f e
+> type SEffect f e = Effect f (SPResult e)
 
 > -- | Simple processor result type.
 
@@ -206,20 +206,16 @@
 > -- | A processor that delivers the entire input of the stream folded
 > --   into a single value using the supplied right-associative function
 > --   and initial value.
+> --
+> --   Note that this can be quite inefficient for long streams, since
+> --   the entire chain of applications of 'f' needs to be materialised
+> --   on the heap before it can ever be applied to the final value and
+> --   reduced at the end of the stream.
 
 > spfoldr :: (a -> b -> b) -> b -> SQ a x f b
-> spfoldr f = cloop
->  where
->   cloop r = spconsume (cloop . flip f r) (deliver r)
-
-> -- | A processor that delivers the entire input of the stream folded
-> --   into a single value using strict application of the supplied
-> --   right-associative function and initial value.
-
-> spfoldr' :: (a -> b -> b) -> b -> SQ a x f b
-> spfoldr' f = cloop
+> spfoldr f r = cloop id
 >  where
->   cloop r = r `seq` spconsume (cloop . flip f r) (deliver r)
+>   cloop k = spconsume (\a -> cloop (k . f a)) (deliver (k r))
 
 > -- | A processor that applies a monadic function to every input
 > --   element and emits the resulting value.