Implement ScalarLoop grad #300
Description
@aseyboldt mentioned we should be able to implement the gradient as another ScalarLoop, via forward auto-diff, which in this case should be equivalent to backward-autodiff.
It should also be possible to fuse the loops, but hopefully that's one thing the compilers can easily figure out, once they get merged inside the same Composite?
Originally posted by @ricardoV94 in #283 (comment)