Verify and comment that addTarget gets duplicable arguments

src/HordeAd/Core/Delta.hs

@@ -255,6 +255,8 @@ addRepM a b = case (a, b) of
   (MTKScalar ta, MTKScalar tb) -> MTKScalar $ ta + tb
   (MTKR ta, MTKR tb) | STKR _ STKScalar{} <- stensorKind @y -> MTKR $ ta + tb
   (MTKR ta, MTKR tb) -> MTKR $ addTarget stensorKind ta tb
+    -- target has a ShareTensor instance, so ta and tb don't need
+    -- to be duplicable
   (MTKScalarDummy, _) -> b
   (_, MTKScalarDummy) -> a
   (MTKRDummy{}, _) -> b
@@ -1132,6 +1134,8 @@ evalRev !s !c d0 = case d0 of
     $ case DMap.lookup n $ nMap s of
         Just _ ->
           let addc x = RepAD $ addTarget stensorKind c (unRepAD x)
+            -- target has a ShareTensor instance, so addTarget arguments
+            -- don't need to be duplicable
           in s {dMap = DMap.adjust addc n $ dMap s}
         Nothing ->
           let cd = RepAD c

src/HordeAd/Core/OpsConcrete.hs

@@ -126,6 +126,8 @@ instance BaseTensor RepN where
       let l = runravelToList t
           sh = shrTail $ rshape t
       in foldr (addTarget stensorKind) (constantTarget 0 (FTKR sh x)) l
+        -- RepN has a ShareTensor instance, so addTarget arguments
+        -- don't need to be duplicable
   rsum0 t = case tftk stensorKind t of
     FTKR _ FTKScalar ->  -- optimized
       RepN . Nested.rscalar . Nested.rsumAllPrim . unRepN $ t