X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FFoldable.hs;h=c44f0cd1c80c428fa728cf063e360fefd450bccc;hb=487b9d4571a847ee0273b4627aaa135c46a51b8d;hp=ed05a165a10c8f5b8d6cce781090ac81dd506c06;hpb=dbe9d53f7f98fb0de5d6d8d8c83c496a119f8653;p=ghc-base.git

diff --git a/Data/Foldable.hs b/Data/Foldable.hs
index ed05a16..c44f0cd 100644
--- a/Data/Foldable.hs
+++ b/Data/Foldable.hs
@@ -96,7 +96,12 @@ import Array
 -- >    foldMap f (Node l k r) = foldMap f l `mappend` f k `mappend` foldMap f r
 --
 -- This is suitable even for abstract types, as the monoid is assumed
--- to satisfy the monoid laws.
+-- to satisfy the monoid laws.  Alternatively, one could define @foldr@:
+--
+-- > instance Foldable Tree where
+-- >    foldr f z Empty = z
+-- >    foldr f z (Leaf x) = f x z
+-- >    foldr f z (Node l k r) = foldr f (f k (foldr f z r)) l
 --
 class Foldable t where
         -- | Combine the elements of a structure using a monoid.
@@ -157,6 +162,9 @@ instance Foldable [] where
 
 instance Ix i => Foldable (Array i) where
         foldr f z = Prelude.foldr f z . elems
+        foldl f z = Prelude.foldl f z . elems
+        foldr1 f = Prelude.foldr1 f . elems
+        foldl1 f = Prelude.foldl1 f . elems
 
 -- | Fold over the elements of a structure,
 -- associating to the right, but strictly.