You may be interested in this paper too https://arxiv.org/abs/1711.10455

I think given a language with AD you already don't need to have a separate language for graph building and my understanding is that's one of the goals for the Julia team and I've seen other nice looking packages for AD in other languages

* https://fluxml.ai/2019/02/07/what-is-differentiable-programm...

* http://diffsharp.github.io/DiffSharp/examples-inversekinemat...

I'm also very excited about being able to design neural nets using ideas from functional programming. I love the Keras API but I don't think it's going to be the obvious API a couple of years down the line.