It is easy to use withNameScope/withDevice incorrectly with pure ops

[fkm3]

If you do something like

TF.withNameScope "foo" $ return $ TF.add 1 2

it will not set the name scope of the add op as expected. You have to use TF.render instead of return.

Another, trickier example is discussed here https://github.com/tensorflow/haskell/pull/11#discussion_r85443322