Merge pull request #125 from andrewthad/fix_example_instances

Fix example instances

Author: tibbe

Data/Hashable/Lifted.hs

@@ -43,18 +43,18 @@ import Data.Hashable.Class
 -- > instance (Hashable w, Hashable1 m) => Hashable1 (WriterT w m) where
 -- >     liftHashWithSalt h s (WriterT m) =
 -- >         liftHashWithSalt (liftHashWithSalt2 h hashWithSalt) s m
--- > instance (Hashable1 f, Functor f) => Hashable1 (Free f) where
+-- > instance Hashable1 f => Hashable1 (Free f) where
 -- >     liftHashWithSalt h = go where
 -- >         go s x = case x of
 -- >             Pure a -> h s a
--- >             Free p -> liftHashWithSalt go p
+-- >             Free p -> liftHashWithSalt go s p
 --
 -- The 'Hashable' instances for these types can be trivially recovered with
 -- 'hashWithSalt1':
 --
 -- > instance (Hashable w, Hashable1 m, Hashable a) => Hashable (WriterT w m a) where
 -- >     hashWithSalt = hashWithSalt1
--- > instance (Hashable1 f, Hashable a) => Hashable1 (Free f a) where
+-- > instance (Hashable1 f, Hashable a) => Hashable (Free f a) where
 -- >     hashWithSalt = hashWithSalt1
 
 --

examples/Main.hs

@@ -1,5 +1,6 @@
 {-# LANGUAGE DeriveGeneric #-}
 import Data.Hashable
+import Data.Hashable.Lifted
 import GHC.Generics (Generic)
 
 data Foo
@@ -25,3 +26,25 @@ main = do
   print . hash $ Foo2 "hello" ()
   putStrLn "Hashing Bar"
   print . hash $ Bar 55.50 9.125
+
+-----------------------------------
+-- Higher Rank Hashable Examples --
+-----------------------------------
+
+newtype WriterT w m a = WriterT { runWriterT :: m (a, w) }
+data Free f a = Pure a | Free (f (Free f a))
+
+instance (Hashable w, Hashable1 m) => Hashable1 (WriterT w m) where
+    liftHashWithSalt h s (WriterT m) =
+        liftHashWithSalt (liftHashWithSalt2 h hashWithSalt) s m
+instance Hashable1 f => Hashable1 (Free f) where
+    liftHashWithSalt h = go where
+        go s x = case x of
+            Pure a -> h s a
+            Free p -> liftHashWithSalt go s p
+
+instance (Hashable w, Hashable1 m, Hashable a) => Hashable (WriterT w m a) where
+    hashWithSalt = hashWithSalt1
+instance (Hashable1 f, Hashable a) => Hashable (Free f a) where
+    hashWithSalt = hashWithSalt1
+