Expand Rendered class to support ResourceHandle wrappers like Variable

This allows functions like `feed`, `colocateWith`, and (in a later commit)
`gradients` to work with `Variable`.

tensorflow-ops/src/TensorFlow/EmbeddingOps.hs

@@ -46,7 +46,7 @@ import qualified TensorFlow.GenOps.Core as CoreOps
 -- tensor. The returned tensor has shape `shape(ids) + shape(params)[1:]`.
 embeddingLookup :: forall a b v1 v2 m .
                    ( MonadBuild m
-                   , Rendered v1
+                   , Rendered (Tensor v1)
                    , TensorType a
                    , OneOf '[Int64, Int32] b
                    , Num b

tensorflow-ops/src/TensorFlow/Gradient.hs

@@ -117,7 +117,7 @@ type GradientCompatible a =
 
 -- | Gradient of @y@ w.r.t. each element of @xs@.
 gradients :: forall a v1 v2 m . ( MonadBuild m
-                              , Rendered v2
+                                , Rendered (Tensor v2)
                                 , GradientCompatible a
                                 )
           => Tensor v1 a  -- ^ The output of the graph.

tensorflow-ops/src/TensorFlow/Ops.hs

@@ -241,7 +241,7 @@ zeroInitializedVariable'
 zeroInitializedVariable' params = initializedVariable' params . zeros
 
 -- TODO: Support heterogeneous list of tensors.
-save :: forall a m v . (Rendered v, MonadBuild m, TensorType a)
+save :: forall a m v . (Rendered (Tensor v), MonadBuild m, TensorType a)
         => ByteString    -- ^ File path.
         -> [Tensor v a]  -- ^ Tensors to save.
         -> m ControlNode

tensorflow-ops/src/TensorFlow/Variable.hs

@@ -30,13 +30,16 @@ import TensorFlow.Core
 import TensorFlow.Build (opDef)
 import TensorFlow.BuildOp (buildInputs, pureOp, OpParams)
 import TensorFlow.Output (opInputs, unNodeName)
-import TensorFlow.Tensor (tensorNodeName)
+import TensorFlow.Tensor (Rendered(..), tensorNodeName)
 import TensorFlow.Types (tensorType)
 import qualified TensorFlow.GenOps.Core as CoreOps
 import TensorFlow.Ops (zeros)
 
 newtype Variable a = Variable (Tensor Value ResourceHandle)
 
+instance Rendered Variable where
+    renderedOutput (Variable v) = renderedOutput v
+
 -- | Creates a new, uninitialized variable.
 variable :: (MonadBuild m, TensorType a) => Shape -> m (Variable a)
 variable = variable' id

tensorflow/src/TensorFlow/BuildOp.hs

@@ -126,13 +126,13 @@ recordResult = do
     put $! ResultState (i+1) ns
     return $! output i o
 
-instance Rendered v => BuildResult (Tensor v a) where
+instance (TensorKind v, Rendered (Tensor v)) => BuildResult (Tensor v a) where
     buildResult = Tensor . pure <$> recordResult
 
 instance BuildResult ControlNode where
     buildResult = ControlNode <$> ask
 
-instance (Rendered v, TensorTypes as) => BuildResult (TensorList v as) where
+instance (TensorKind v, Rendered (Tensor v), TensorTypes as) => BuildResult (TensorList v as) where
   buildResult = loop (tensorTypes :: TensorTypeList as)
     where
         loop :: TensorTypeList bs -> Result (TensorList v bs)

tensorflow/src/TensorFlow/Tensor.hs

@@ -13,6 +13,7 @@
 -- limitations under the License.
 
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE GADTs #-}
@@ -89,19 +90,16 @@ data Feed = Feed Output FFI.TensorData
 
 -- | A class ensuring that a given tensor is rendered, i.e., has a fixed
 -- name, device, etc.
-class TensorKind v => Rendered v where
-    rendered :: v a -> a
+class Rendered t where
+    renderedOutput :: t a -> Output
 
-instance Rendered Value where
-    rendered = runValue
+instance Rendered (Tensor Value) where
+    renderedOutput = runValue . tensorOutput
 
-instance Rendered Ref where
-    rendered = runRef
+instance Rendered (Tensor Ref) where
+    renderedOutput = runRef . tensorOutput
 
-renderedOutput :: Rendered v => Tensor v a -> Output
-renderedOutput = rendered . tensorOutput
-
-tensorNodeName :: Rendered v => Tensor v a -> NodeName
+tensorNodeName :: Rendered t => t a -> NodeName
 tensorNodeName = outputNodeName . renderedOutput
 
 
@@ -110,7 +108,7 @@ tensorNodeName = outputNodeName . renderedOutput
 --
 -- Note that if a 'Tensor' is rendered, its identity may change; so feeding the
 -- rendered 'Tensor' may be different than feeding the original 'Tensor'.
-feed :: Rendered v => Tensor v a -> TensorData a -> Feed
+feed :: Rendered t => t a -> TensorData a -> Feed
 feed t (TensorData td) = Feed (renderedOutput t) td
 
 -- | Create a 'Tensor' for a given name.  This can be used to reference nodes
@@ -129,7 +127,7 @@ tensorRefFromName = tensorFromName
 
 type TensorList v = ListOf (Tensor v)
 
-tensorListOutputs :: Rendered v => TensorList v as -> [Output]
+tensorListOutputs :: Rendered (Tensor v) => TensorList v as -> [Output]
 tensorListOutputs Nil = []
 tensorListOutputs (t :/ ts) = renderedOutput t : tensorListOutputs ts
 
@@ -137,7 +135,7 @@ tensorListOutputs (t :/ ts) = renderedOutput t : tensorListOutputs ts
 -- device as the given Tensor (see also 'withDevice'). Make sure that
 -- the action has side effects of rendering the desired tensors. A pure
 -- return would not have the desired effect.
-colocateWith :: (MonadBuild m, Rendered v) => Tensor v b -> m a -> m a
+colocateWith :: (MonadBuild m, Rendered t) => t b -> m a -> m a
 colocateWith t x = do
     d <- build $ Device . (^. device)
                <$> lookupNode (outputNodeName $ renderedOutput t)
@@ -184,10 +182,10 @@ class Monad v => TensorKind v where
     toBuild :: v a -> Build a
 
 instance TensorKind Value where
-    toBuild = return . rendered
+    toBuild = return . runValue
 
 instance TensorKind Ref where
-    toBuild = return . rendered
+    toBuild = return . runRef
 
 instance TensorKind Build where
     toBuild = id