Merge pull request #172 from sjshuck/product-instance-methods

Explicit method impls for MonadState and MonadWriter Product instances

Author: sjshuck

Control/Monad/State/Class.hs

@@ -197,3 +197,4 @@ instance MonadState s m => MonadState s (SelectT r m) where
 instance (MonadState s m, MonadState s n) => MonadState s (Product m n) where
     get = Pair get get
     put s = Pair (put s) (put s)
+    state sas = Pair (state sas) (state sas)

Control/Monad/Writer/Class.hs

@@ -208,6 +208,7 @@ instance
     pass   = Accum.liftPass pass
 
 instance (MonadWriter w m, MonadWriter w n) => MonadWriter w (Product m n) where
-    tell w = Pair (tell w) (tell w)
+    writer aw           = Pair (writer aw) (writer aw)
+    tell w              = Pair (tell w) (tell w)
     listen (Pair ma na) = Pair (listen ma) (listen na)
     pass (Pair maf naf) = Pair (pass maf) (pass naf)