I am using Julia 1.3, Flux 0.9 (somehow my flux doesn’t update to 0.10).
Your guess was correct; this network is useless since Flux can’t find any parameters, therefore cannot adjust these parameters with backpropagation. I’m guessing I made some silly mistake thanks to my inexperience using Flux!
In Flux 0.10 @treelike is replaced by @functor, but as far as I could see this should not change functionality.